Aquarium Setup #5 – April 1993

Air Pumps

 by Dr. Steven J. Schiff

 

            If you had to rate aquarium hardware by its sex appeal, the lowly air pump would be near the bottom of the list.  It wouldn’t be as far down as, say, feeding rings or tank dividers, but it’s safe to say that most aquarists don’t get totally turned on by an air pump.  I’m sure that if Porsche designed air pumps, this would be different, but unfortunately they don’t, so try to remain calm.

            Air pumps, despite their relative absence of sex appeal, are one of the most ubiquitous accessories utilized by aquarists.  What they lack in physical attractiveness, they more than make up in aquacultural usefulness.  They can be found lurking near almost every fish tank in the world.  All too often, though, they are purchased as an afterthought or without much advance planning.  As is the case with almost all aquarium equipment, careful selection and setup of the air pump will result in maximum performance, longer life, and lowest-cost operation.

            There are three major categories of air-pumping devices used in the majority of home aquarium setups.  For the largest installations involving multiple tanks and lots of air, there are rotary air blowers.  These provide the greatest volume of air and can serve dozens of tanks simultaneously.  They are noisy and consume a fair amount of electricity, so they are used only when the sheer number of tanks and amount of air required warrants it.

            Piston pumps form the second category.  These were very popular several decades ago, when their pumping volume and pressure could not be matched by the noisy and underpowered vibrator pumps that were their chief alternative.  Piston pumps are still available in both one and two cylinder models, but they have largely been superseded by the vastly improved vibrator pumps which form the third category.  No longer noisy or underpowered, vibrator pumps are available in a wide variety of models, sizes, and designs.  Their high performance and (generally) low cost makes them the overwhelming choice for home aquarium use.

            In selecting a pump for your particular setup, you should choose one that can provide enough air to run all the air-driven accessories in all the tanks it will be servicing, and then some.  It is better to buy a pump that’s too big for a given application than one that’s too small.  The output of a larger pump can always be reduced to a lower level if necessary, but an underpowered pump will never give satisfactory performance and will have to be replaced.

            One problem in choosing an air pump is that there are no uniform standards for rating them.  Some manufacturers rate their pumps by the pressure delivered; others by the volume of air.  A few indicate what size tank or how many accessories can be served by a particular model.  This latter system would be very useful if it were uniformly applied, but different manufacturers have different ideas of how much air is required by a given tank, or how many accessories will be used in a tank.  Unfortunately, all too many manufacturers give no idea at all about the output of their pumps.

            Ideally, the output of an air pump would be rated by both volume and pressure.  A high-volume pump is useless if it cannot deliver its air against the pressure produced by the water in the aquarium.  Similarly, a pump that cannot deliver a sufficient volume of air is inadequate, even if it produces high pressure.  With your specific setup in mind, you can decide on a pump by enlisting the aid of your aquarium dealer, who can help you decide how much air you need, and which pumps will provide it.

            Two factors affect the back pressure which must be overcome by an air pump which is forcing air through an air-line tube and into an underwater accessory (such as an airstone.)  The first is the water depth, i.e., how far underwater is the accessory?  This determines the water pressure that must be overcome by the pump in order to force air through the tube.  It is independent of the accessory.  In a 10 gallon tank, the water depth is 12 inches, and the water pressure at the bottom of the tank is 0.45 lb. per square inch.  In a 55 gallon tank that is 18 inches deep, the water pressure is 0.68 lb. per square inch.  Even at a depth of four feet, the water pressure is less than two pounds per square inch.  These pressures are easily overcome by aquarium air pumps.  A typical high-output vibrator pump, for example, can exert 7.5 pounds per square inch.  Smaller pumps develop less pressure, of course, but should have no trouble pumping air to the bottom of any home aquarium.

            The other factor, of course, is the accessory itself: how hard is it to force air through the airstone?  This varies from accessory to accessory and is more difficult to quantify.  In general, though, the smaller the opening through which air must be forced, the greater the pressure required.  In addition, the pressure required to run the accessory usually increases with time, as the air passages become clogged and dirty.  Not only does this reduce the air flow and decrease water movement, it can actually damage the pump!  The diaphragm of many vibrator pumps can tear if the back pressure becomes excessive.  For this reason, it is important to keep your air-driven accessories clean, and change the disposable ones when the airflow becomes visibly reduced.  (One common test: change an airstone when you can no longer blow through it by mouth.  However, I suspect that pump damage can occur even before airflow resistance becomes this high.  So change your airstones before you think you need to.)

            Assuming you don’t have an enormous fishroom that requires the services of a rotary blower or similar specialized air supply, your choice is essentially going to be between a vibrator and a piston pump.  Although the vibrator type is the overwhelming choice today, let’s not dismiss the piston out of hand, but carefully evaluate the advantages and disadvantages of each.

            1.) Noise.  No air pump is completely silent, but some of the better-made vibrator pumps (especially in the smaller sizes) are very quiet.  Piston pumps have very quiet motors, but the operation of the piston produces a bit more noise.  Overall, a properly operating piston pump should not be any more noticeable than the low hum of a vibrator pump of comparable output.  Modern air pumps of either type are not particularly noisy.

            2.) Cost.  Because there is such a wide variety of vibrator pumps available, it is difficult to generalize (since when has that stopped me?)  The price of these pumps varies with size, quality of construction, and reputation of manufacturer.  In general (see?), a vibrator pump will cost somewhat less than a piston pump of comparable output.

            3.) Ease of repair and maintenance.  Normal maintenance (which I will discuss shortly) of both types of pumps is easy to perform and can be done by most aquarists, even those who are not mechanically inclined.  This is also true of the most common types of repairs required on vibrator pumps..  If the motor of a piston pump requires repair, however, it is no simple task.  (Fortunately, these motors are very durable.)

            4.) Availability of spare parts.  While this is usually not a problem for any brand of pump still in production, the widespread availability and enormous popularity of vibrator pumps gives them an advantage in this area: many pet shops keep frequently-used parts and repair kits in stock.

            5.) Vibration.  As their name implies, vibrator pumps vibrate.   While it usually doesn’t lead to excessive noise, this vibration can cause the pump to “walk” or gradually creep across the surface on which it rests.  These pumps usually have flexible “feet” on their bases which are intended to dampen the vibration and minimize this problem, with varying degrees of effectiveness.  Piston pumps usually don’t suffer from this.

            6.) Electrical consumption.  The motor of a vibrator pump has but a single moving part and is very efficient.  A typical medium-to-high output vibrator pump consumes 5 watts of power; a typical piston pump of comparable output consumes about 11 watts.  In addition, the more complex motor of the piston pump produces a significant amount of heat — enough so that good ventilation is a consideration when installing such a pump.

7.) Output.  The piston pumps that are currently available all have a fairly hefty output, both in terms of pressure and volume.  To run a small aquarium – one or two airstones, a box or sponge filter, etc. – they are overkill.  There are many small vibrator pumps that will perform this task efficiently, quietly, and at low cost.  When a higher output is needed, of course, a piston pump is a viable alternative to a vibrator, and the two should be compared according to the features that most affect your own situation.

            As with most mechanical equipment, proper maintenance of your air pump will enable it to last longer and operate more efficiently.  There are simple maintenance procedures that are required for each type of pump.  The motor of a piston pump should be oiled regularly and kept free of dust.  Keep it away from flammable substances because it can get hot.  The leather washer that caps the piston should be changed occasionally to maintain an airtight seal.  The external drive belt wears and may periodically require replacement.

            In a vibrator pump, the diaphragm wears and eventually tears, whereupon it must be replaced.  Excessive back pressure (as from failure to change airstones) can hasten this process.  The valves wear out and must occasionally be replaced.  If the pump has an air filter, the filter should be replaced when it becomes dirty.  All of these operations can be performed without a high degree of mechanical aptitude.

            Some vibrator pumps have a rotary control that regulates the output.  These make it very easy to control air flow and deliver precisely what you need to your system.  If your pump lacks such a control, you may still regulate the air flow by inserting a valve in the air line that bleeds off as much air as necessary.

            Unlike much aquarium equipment (such as heaters, filters, lights, etc.), the location of an air pump is not terribly critical.  You can put it anywhere nearby the tank (as long as it is not in the tank).  Very long runs of airline tubing may reduce the output somewhat, but this is rarely a problem.  If the pump is located below water level, however, it is a good idea to install a check valve in the air line.  This is a valve that allows air to pass one way in the line, but closes if the direction of flow becomes reversed.  If a pump located below water level should fail, an somehow water finds its way to the highest point of the tube, a siphon can start which will allow water to run out of the tank until the siphon is broken.  If your accessory (an airstone, for example) is located near the bottom of the tank (the most efficient placement for an airstone), the tank can be nearly emptied in this way.  This is not conducive to fish health, and a check valve is effective, inexpensive insurance against it.

Basics of Filtration

 

Aquarium Setup #4 – March 1993

Basics of Filtration

 

by Dr. Steven J. Schiff

 

            Life is full of choices.  In fact, much of life consists of making decisions and living with the conse­quences of those decisions.  For example, we have all made the decision to become aquarists.  Having done so, we find ourselves faced with myriad further choices to make: Fresh or salt water?  Fish or inverte­brates?  Flake food or pellets?  Shall I do a water change or lie on the couch, watch TV, and think about doing a water change?  (Some choices are easier than others.)  Each of these decisions, of course, leads to endless new ones (for example, what show should I watch while I an lying on the couch thinking about doing a water change?)

            This article is intended to make one of your choices easier.  The decision to be made, in this case, is what filtration to use in a given aquarium.  While I can’t make that decision for you, I can provide information that will permit you to make an informed choice within the constraints imposed by your own particular situation.

            A very broad definition of filtration is “the treatment of aquarium water to make it more liveable for fish.”  We can add to this by saying that we must pass the water through some kind of device to perform the treatment.  This column will help begin­ning aquarists understand the basics of filtration and review the fundamental principles of aquarium filters, as well as some common products that incorporate these principles.

            We generally speak of three major types of filtration: mechanical, chemical, and biological.  Most filters provide at least two of these types, and some provide all three.  Different filter types are better at some types of filtration and worse at others.  Our task as aquarists is to select the appropriate equipment to do the desired job.

                                                              Mechanical Filtration

             Mechanical filtration is what we usually think of first when we talk about filtration–this is what keeps the water “clean”.  Most filters provide at least some mechanical filtration, but again, some do it better than others.

            In most aquaria, outside power filters are the best type for mechanical filtration.  They provide a high water flow rate, which circulates the water thoroughly and thus removes solid waste material before it can decay and foul the water.

            For efficient mechanical filtration, we need at least two tank turnovers per hour – that is, the entire volume of water in the aquarium should pass through the filter at least twice per hour.  This is really a bare minimum – we are much better off with four or five hourly turnovers, and even as many as ten is not excessive in most cases.  (Instances in which this much water flow would be excessive include tanks of fry or slow-moving fish, such as long-finned fancy goldfish.)

            No common filter types other than outside power filters provide such a high flow rate at reasonable cost.  Other filters, such as inside power, canister, sponge, and box filters, also perform mechanical filtration, but their smaller size and/or lower flow rates tend to make them less effective.  Therefore, they should be carefully matched to the tank size and particular application for which they are to be used.

            The diatom filter is a special type designed for mechanical filtration only.  The filter medium is diatom powder, which consists of the skeletons of microscopic algae-type plants.  These form an extremely fine sieve which can catch particles as small as one micron (one millionth of a meter, or a thousandth of a millimeter).  The filter thus removes all particulate matter larger than bacteria, and produces extremely clear water.  Because of this extremely fine filtering capability, diatom filters clog quickly and are not intended for continuous use.  Rather, they are employed occasionally to “polish” the water and remove the free-swimming larval stages of parasites such as Ichthyophthirius (“ich”).

                                                                Chemical Filtration

             Mechanical filtration removes particles from the water, but doesn’t change its chemical makeup.  Chemical filtration actually changes the chemical characteristics of the water.  We do this for two reasons: 1) to remove toxic substances or waste products from the water, and 2) to alter the water to make it more suit­able for a particular type of fish we want to keep.  For example, if we wish to raise discus or neon tetras (which require soft, acidic water) and our tap water is hard and alkaline, we can use chemical filtration to soften the water and lower its pH.

            Chemical filtration usually involves passing the water over a medium which alters its chemistry.  Some such media include:

            • Dolomite or crushed coral - increase hardness and pH.

            • Zeolite - removes ammonia.

            • Activated carbon - removes organic substances, medica­tions, dyes, etc., via adsorption onto its huge surface area.

            • Peat - decreases hardness and pH.  Also adds beneficial substances to the water, such as tannins and humic acid.

            These substances are placed in a filter, and the water is altered as it flows over them.  Canister filters are particularly good for this purpose, as they will hold more filter media than most other types.

            Another, more specialized type of chemical filter is the foam fraction­ator, or “protein skimmer”.  This device works almost like activated carbon, removing organic substances, dyes, medications, etc., by adsorption onto the surface of enormous numbers of very small bubbles.  As with activated carbon, surface area is the key.  Foam fractionation works better in salt water than in fresh water; as a result, these devices are usually found in marine aquarium systems.

                                                                Biological Filtration

             Biological filtration is probably the most important of the three major types of filtration, as well as being the least understood.  It is not difficult to accomplish.  It involves growing as large a population of beneficial nitrifying bacteria as possible by providing the proper condi­tions.  These bacteria live by breaking down certain nitrogenous waste products produced by the fish; in doing so, they convert these toxic substan­ces into less harmful forms.

            As shown in Figure 1, the first step in biological filtra­tion is the breakdown of ammonia into nitrite by bacteria of the genus Nitrosomonas.  Ammonia is excreted directly into the water from the fishes’ gills.  It is also a breakdown product of their urine, solid waste, uneaten food, and any other nitrogen-contain­ing organic materials in the tank.  It is quite toxic to fish, but a properly functioning biological filter can break it down as fast as it is produced.

            The product of the breakdown of ammonia is nitrite.  Unfor­tunately, this is still rather toxic to fish.  Fortunately, the other bacteria in the biological filter, genus Nitrobacter, use nitrite as food, and break it down into nitrate, which is rela­tively nontoxic.  The concentration of nitrate in the water can go quite high before affecting the fish, but it eventually does cause problems.  For this reason, we perform regular, partial water changes, which dilute the nitrate and keep its concentra­tion at safe levels.  I don’t think we can emphasize the impor­tance of water changes enough.  Failure to do them probably results in more failures in keeping fish than any other problem.

            Nitrobacter and Nitrosomonas bacteria do not float freely in the water, but must attach to a solid surface.  The purpose of a biological filter medium is to provide as much surface area for bacterial attachment as possible, while allowing free flow of water over the medium (i.e., not clogging).  Some examples of biological filter media include:

            • Filter floss – very large surface area.  Inexpensive, but clogs easily.  When discarded, the bacteria living in it are discarded too, reducing the effectiveness of the biological filter.

            • Sponge or foam – good surface area.  Reusable and inexpen­sive.  Rinsing in aquarium water outside the tank will remove dirt without signifi­cantly impairing biological effectiveness.

            • Woven nylon pads – good surface area.  Reusable and easier to clean than a sponge; less likely to clog.

            • Ceramic rings or “noodles” – moderate surface area.  Heavy but extremely durable.  Don’t clog easily.

            • Specialized “biological” media – included in this category are all the products intended specifically and exclusively as biological filtration media, such as BioChem Beads^R and Stars, BioBalls^TM, Bio-Blocks^TM, Bio-Pak^R, etc.  There are many compet­ing products in this category, and a lot of advertising claims are made for them.  In evaluating these claims, we must keep in mind the basic purpose of the medium and use the information presented here and elsewhere to make an informed decision.

            Nitrification (the stepwise conversion of ammonia to ni­trate) is an aerobic process, which means that Nitrobacter and Nitrosomonas require oxygen to perform their functions.  This is why so-called trickle or wet/dry filters work so well.  They provide, better than other designs, the three elements that are essential for growing these bacteria:

            1) Large surface area (these are the largest filters gener­ally used on home aquaria);

            2) Constant, gentle flow of nutrient-rich water - the prolonged contact time of the water with the media allows the bacteria to completely remove ammonia and nitrite; and

            3) Water flowing over the bacteria is saturated with oxygen.  In a wet/dry filter the media are not immersed in water, but rather are coated with a thin film of it as it trickles over them.  This is enough to keep the bacteria wet, and the close proximity of air ensures that dissolved oxygen is at a maximum.

                                                             Common Filter Designs

             As I mentioned earlier, each type of filter performs differ­ently with respect to the three major types of filtration.  Choosing a filter for a given aquarium requires knowledge of the strengths and weaknesses of each type.  For example, a tank set up with both an outside power filter and an undergravel filter would benefit from the excellent biological filtering performance of the undergravel filter, as well as the superior mechanical filtration effec­tiveness of the power filter.  Combining filtra­tion methods in this manner is a superb technique for custom-tailoring a particular installa­tion to precisely meet its re­quirements, while using readily-available existing products.  The following guide rates some familiar designs with respect to biological filtration ability (BFA), mechani­cal filtration ability (MFA), and chemical filtration ability (CFA):

             • Box filters are simple and basic.  Filter floss provides mechanical filtration and surface area for biological filtration.  They can be filled with chemical media such as carbon, crushed coral, ammonia-removing resins, etc.  These are good all-around filters for small tanks.

            BFA: Good.

            MFA: Fair (flow rate too low).

            CFA: Good.

 

            • Sponge filters are excellent for fry tanks.

            BFA: Excellent (high surface area).

            MFA: Fair (flow rate too low).

            CFA: None.

 

            • Canister filters are extremely versatile.

            BFA: Excellent.  Can be filled with almost any medium or combination of media.  The prolonged contact time between the water and the media and the high media volume promotes complete nitrification of ammonia.

            MFA: Fair to good (depends on flow rate).

            CFA: Excellent, due to the large media volume and wide choice of available media.

 

            • Outside power filters are among the most commonly used designs.

            BFA: Fair to good, depending on flow rate and media volume.

            MFA: Excellent.

            CFA: Good.  Varies with media volume.

 

            • Diatom filters produce very clean water very quickly, and are often moved from tank to tank to clear up the water in each one.

            BFA: None.

            MFA: Excellent.  Gets water very clean, but clogs quickly.

            CFA: Limited.  Can be used with activated carbon powder, but effective chemical filtration often requires more time than these filters are given.

 

            • Undergravel filters are often thought of as being synonym­ous with biological filters.  We have seen that other types of filters can perform this function; however, undergravel filters do it very well because they provide a very large surface area and a fairly slow water flow, giving the bacteria time to do their work.

            The filter medium is actually the gravel in the tank, which acts as a substrate for bacterial attachment.  If crushed coral or dolomite is used instead of gravel, chemical filtration can occur, but the options are limited.  Mechani­cal filtration ability is also limited, as sucking the dirt down into the gravel doesn’t really qualify as cleaning the tank.

            BFA: Excellent.  Simple and inexpensive.

            MFA: Poor.

            CFA: Limited.

 

            • Trickle filters, although not yet very common, are rapidly increasing in popularity due to their superb performance and advanced technology.  They tend to be rather bulky and expensive, and are usually used on larger tanks.

            BFA: Excellent.

            MFA: Fair to good, depending on flow rate.

            CFA: Excellent.

 

Heaters

 (This article was originally published in February 1993.)

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Heaters

One of the basic elements of any aquarium setup to maintain tropical fish is a thermostatic heater.  When such a heater is working properly, it’s easy to forget that it’s even there.  This is a tribute to the reliability of modern heater designs, of course, and I for one appreciate their maintenance-free construction.  However, because they’re so easily forgotten, any problems that do occur can progress to the point where the health of your fish is endangered before you discover that something is wrong.  For this reason, it’s important to monitor the performance of your heaters and take proper care in their setup.

Although a number of designs are available, most of today’s aquarium heaters consist of a sealed glass tube which encloses heating elements and circuitry, including a self-contained thermostat.  There are two main types: hanging and submersible.  The former type hangs vertically from the top rim of the aquarium with the glass tube immersed in the water.  The latter type can be placed anywhere in the aquarium as long as most of the glass tube is below water level.  They are often attached to the aquarium glass with suction cups, and can be positioned vertically or horizontally, deep or shallow, depending on the particular setup.  Obviously, these are more versatile than the older, hanging style, but they are also more expensive.

The thermostat in an aquarium heater senses the water temperature and turns the heating element on when it drops below a certain preset level.  As the temperature rises above this level, the thermostat shuts the heater off.  The accuracy of this process varies among heater brands and models, but it is generally sufficient to maintain water temperature constant to within ±1°F, which is steady enough to cause no harm to fish.  Many brands advertise accuracy to within ±¼°F, which is far less fluctuation than most species experience in the wild!  Keep in mind that in nature, most fish do not live in a temperature-controlled environment.  Water temperature varies from sun to shade, deep water to shallow, day to night, and season to season.  It also varies with weather, often dropping when it rains.  As long as the temperature remains withing an appropriate range and any changes are gradual, small fluctuations (plus or minus a degree or so) will not affect healthy fish.

The most important factor to consider when selecting a heater is its power output.  If this is too low, it will not keep the tank warm enough, nor maintain a stable, uniform temperature.  If too high, it costs more than necessary, and any increases you make in the temperature will occur too rapidly.  In addition, if an overpowered heater sticks in the ON position, it can rapidly cook the fish.

Heater power is based on tank size.  A useful estimate of the power required in temperate climates is 3-5 watts per gallon of water to be heated.  I have found the lower end of this range to be perfectly adequate; however, in cooler climates (or if the tank temperature must be maintained more than about 10°F above room temperature), it would be desirable to provide 5 watts per gallon or even more.  As an example, a 50 gallon tropical tank kept at 78°F in a room kept at 68°F will require 150 watts of heater power; if located in a basement at 58°F, 250 watts or more will be needed.

Tubular heaters are available in a wide range of powers, from 25 watts right on up to 300 watts.  (For very large systems, 300 gallons or more, there are high-powered heaters available which are not located in the aquarium.  Rather, they are placed in-line with the filtration system and water is pumped through them, being heated as it goes.)  The higher-power tubular units are sufficient to heat tanks up to 100 gallons under normal condition, but I would strongly suggest the use of two half-powered units, especially in larger aquaria.  There are several reasons for this:

            1) Each unit acts as a “fail-safe” for the other.  In the event that one heater fails, any temperature swing that occurs will be smaller and the rate of change will be lower than if a single full-power unit had failed.  For example, if one unit won’t go on , the other will run and keep the temperature from dropping as far or as fast as if no heater remained.  On the other hand, if one sticks in the ON position, the other will run less, and the temperature will rise less (and more slowly) than if the sticking heater was full power.

            2) The two units can be placed far apart in the tank to provide a more even distribution of heat.  If one full-power heater, or both half-power units, are placed at one end of a long aquarium, the tank temperature will not be completely uniform unless there is a very strong water flow in the tank induced by the filtration system (more on this later.)

            3) For very large tanks (say, 125 gallons or more), only the in-line units are made with high enough power output that a single unit can do the job.  In such aquaria, you may utilize this type or multiple heaters of the standard type; if you choose the latter option it is important to select and set them up properly.

Whether you choose a hanging or a submersible type, there are several things you can do to maximize its performance and give your fish the most comfortable, thermally stable environment possible.  First among these is to obtain an accurate thermometer and check the temperature daily.  This is the best indication you will get of the proper operation of your heater, or of its malfunction if that should occur.

Another way to get the most out of your heater is to position it properly within the tank, and to select the unit, when purchasing it, with an eye towards proper positioning.  The heater heats the water that immediately surrounds it, i.e., that which is in direct contact with the glass tube. Water is not a good conductor of heat, and unless this warmed water is circulated throughout the tank, the water temperature in the aquarium will not be uniform.  In the absence of any water circulation, water heated by the heater will rise to the surface and form a layer.  The bottom of the tank will remain significantly cooler.  This stratification may be fine in lakes and oceans, but it is not desirable in an aquarium.

There are two ways to remedy this situation.  Since warm water rises off the heater, you can induce a circulation by locating the heating element as close to the bottom of the tank as possible.  As the heated water rises, cooler water sinks to the bottom to replace it, inducing a convection current in the aquarium.  By itself, this circulation will not be sufficient to keep all parts of the tank at a uniform temperature, but it helps.  It’s easy to place a submersible heater of any size hear the bottom, but how can you do this with a hanging model?  Several of these are available in different lengths — 8", 10", 12", 20", etc.  Select the length that will place the heating element (located near the bottom of the glass tube, farthest from the thermostat control knob) as close to the bottom of the tank as possible.

The other, more effective way to avoid stratification and “hot spots” in the aquarium is to locate the heater directly in the current provided by an airstone or power filter.  The water movement produced in this way thoroughly distributes heated water throughout the tank and ensures a more uniform temperature.  Alternatively, the heater (or heaters) can be located near the intake of a power filter.  Warm water that is drawn into the filter will quickly be spread to all parts of the aquarium.  However, because the current at a point near the intake of a filter is less than that directly in the outflow, this will be somewhat less effective.

Hanging heaters must be installed vertically, but this is not the ideal position (see diagram).  As warm water rises from the heating element, it moves along the tube of a vertically positioned heater and will affect the thermostat.  Proper water circulation will minimize this; however, if you have a submersible heater you can install it in a diagonal or horizontal position.  This may make it a little harder to reach the control knob, but once set, this should rarely have to be touched.

Many submersible heaters have a rubber cap covering the top of the heater and the control knob.  These are used to make the unit waterproof.  I find that they often make them adjustment-proof, as well.  It can be extremely difficult to turn a control knob that is covered with one of these caps, especially when it is wet.  I much prefer the brands that are waterproofed without these troublesome caps.

A number of current heater models have a temperature scale on them to aid in setting the thermostat.  My experience is that while these are useful guides, they are not absolutely accurate.  When installing a heater into a new (cold) tank, place it in the water in a convenient location (not necessarily its final position) where the thermostat control knob can easily be reached.  Be sure there is sufficient water circulation from a filter or airstone to thoroughly distribute the heated water throughout the tank.  Plug the heater in and look for the pilot light.  (If it’s not on, turn the knob until the light comes on.)  If the heater has a temperature scale, turn the dial to a point a few degrees below the desired temperature.  Now check the tank temperature every half hour or so.  When the pilot light begins to cycle on and off, the set temperature has been achieved.  Using the thermometer reading as your guide, make fine adjustments to the knob until the tank has stabilized at the desired temperature.  Be sure to give the tank time to equilibrate before making each adjustment.  (If the heater has no temperature scale, the initial setting above current tank temperature will be a guesstimate.  It’s better to err on the conservative side and have to increase the setting later than to set it too high and have to wait for the temperature to drop before resuming.)  Once this has been achieved, the heater may be moved to its permanent position.

It is not necessary to unplug your heaters during the summer months.  They may not go on very often (unless you have a bodacious air conditioner!), but they will place a floor on the aquarium temperature.  This is the exact reason they’re there, and there is no point in disturbing your careful equilibrium, or in removing your insurance protection.

Once a thermostatic heater is in place and properly functioning, it should be able to maintain a stable aquarium temperature for years without further attention.  This happy state of affairs is far easier to attain if the heater is selected and installed properly at the outset.

Box Filters

 (This article was first published in January 1993.)

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If you’re like most people I know in the aquarium hobby, myself included, you probably started out keeping fish in a 10 gallon tank.  Many novices initially maintain hardy “beginner” fish, such as swordtails, guppies, and platies, which can live quite happily in a tank of this size.  Whatever kind of fish you kept and regardless of how you obtained the aquarium (purchase, gift, hand-me-down, etc.), chances are good that its filtration was provided by an air-driven box filter.  These filters are widely used in beginner’s tanks because they are inexpensive and easy to set up.

Just because they are often associated with such novice setups, however, and because they don’t cost a lot of money, doesn’t mean these filters aren’t any good.  On the contrary: they can do quite a good job if set up properly.  Proper setup and application are important because, despite their virtues, box filters do have certain limitations.

A box filter is actually a miniature canister filter which is driven by air flow instead of an electric water pump.  It shares with its larger brethren the ability to employ a wide variety of filtration media, thus giving it the versatility to provide biological filtration, chemical filtration, or both.  Like a canister filter, it must be located below water level, but because it is placed in the water, it cannot do its job as invisibly or unobtrusively as the canister filter.  On the other hand, it requires but a single, narrow air-line tube, avoiding the more complex hose arrangements of canister filters.

The operation of the box filter is simplicity itself (see diagram.)  Air is pumped to the bottom of a pipe which stands vertically in the center of the filter.  The pipe is raised a short distance above the bottom of the filter box to allow water to enter it from below.  As the air bubbles rise in the pipe, they pull water with them from the bottom of the box.  Water enters the top of the box surrounding the pipe and flows downward to replace the water that has been dragged out of the box by the air bubbles.  As this replacement water flows downward, it passes through the filter medium that has been packed around the ascending pipe.  (The medium is also held a short distance above the bottom of the box by a perforated plate, to allow water to flow freely out of the medium and into the ascending pipe.)

Because they are air-driven, box filters don’t have the high water flow rates of many motor-driven filters.  However, when properly set up, some box filters can attain the quite respectable flow rate of 100 gallons per hour.  Proper setup in this case involves an adequate air pump, an airstone at the air input to the filter, and a “chimney” that extends the ascending pipe several inches.  The small bubbles produced by an airstone provide greater lift than the larger bubbles that come out of an open-ended tube.  The “chimney” increases water flow by extending the time during which the rising bubbles actually pull water through the filter.

A high flow rate, although nice to have, is not essential for the proper operation of a box filter.  What is required is a continuous flow of oxygenated water over the filter media.  This will provide a beneficial environment for the nitrifying bacteria that colonize the surface of the media, oxidizing ammonia to nitrite and then to nitrate, a process known as biological filtration.

The list of potential filter media is long.  The “traditional” packing of a box filter is a layer of activated carbon on the bottom, covered by a layer of filter floss.  Since the floss is on top, the dirty water entering the filter is screened of solid particulate matter (mechanical filtration) before it flows through the carbon layer, which removes many organic chemicals, dissolved gases, dyes, etc. (chemical filtration).  Both the floss and the carbon have enormous surface areas exposed to the water, allowing substantial populations of nitrifying bacteria to colonize them.

Box filters are by no means limited to the use of these two media.  You may break with tradition and put almost anything you want into the box, depending on the effect you want to achieve.  Coral gravel or dolomite can be used to increase pH and hardness.  Peat moss will have the opposite effect.  Plain gravel, ceramic, or plastic media (sponge, floss, etc.) may be used to provide mechanical and biological filtration without otherwise affecting the chemical makeup of the water.  In short, anything you can put into a canister filter can also be used in a box filter.  The only limitations are that it must fit within the small box in sufficient quantity to do some good and it must not be packed so densely that air flow alone cannot draw water through it.

A box filter may be located anywhere in an aquarium, but it will operate most efficiently if placed near the bottom of the tank in an upright position.  This allows the rising bubbles to draw the maximum amount of water through the filter, as well as to circulate water from the bottom to the top of the tank.  This circulation improves aeration of the aquarium water, distributes filtered water throughout the tank, and draws unfiltered water toward the filter.

The mechanical filtration ability of a box filter depends on the rate of water flow through the filter and on the nature of the filter media.  As in any type of aquarium filter, the finer the mesh of the filter medium, the more effective its mechanical filtration ability.  At the same time, the more effective a particular medium is at mechanical filtration, the more easily it becomes clogged.  It is not easy to tell when  a box filter is clogged, as the actual water flow is invisible.  Bubbles continue to stream from a clogged filter, but they are no longer drawing enough water with them.  For this reason, it is a good idea to clean box filters at regular intervals.  (Of course, it’s a good idea to clean any type of filter at regular intervals!)  One visual cue that indicates when to clean a box filter is the appearance of the media: when it looks dirty, it is dirty.

When cleaning a box filter, it’s important to remember that too clean is worse than too dirty.   A dirty filter has loads of nitrifying bacteria clinging to it, doing their job.  Cleaning the filter removes or kills these bacteria; if they are the only source of biological filtration in the tank, the ammonia and nitrite concentrations are likely to rise and the fish will suffer.  If the box filter is the tank’s only filter, you should clean or replace only part of the media (say one-half or two-thirds) at a time.  If you have two box filters, or a box filter and another type, you should only clean one of them at a time.  By alternating your filter maintenance, you assure continuity of biological filtration, which makes for a more stable environment for your fish.

For maximum efficiency, a box filter should be run by an optimal rate of air flow.  (Too much or too little air will both reduce water flow.)  As mentioned earlier, airstones will usually provide greater lift, but they cannot be fit to all box filters, and the filters will work well even without them.  How can you decide on an optimal air flow rate?  Generally, the mixture of water and air exiting the top of the filter should appear to be about half water and half air.  If there are more bubbles than water visible, you should be able to increase water flow by bleeding off some air with a valve, or reducing your air pump’s output rate with a knob (if so equipped.)  If there’s more water than air in the mix (for example, if one bubble escapes the filter before the next one becomes visible), increase the air flow.  If that’s not possible, you need a bigger air pump.

Because of their limited rate of water flow, box filters are generally not suitable for large fish tanks.  Effective mechanical filtration requires a turnover rate of at least 4-5 tank volumes per hour.  A small box filter, properly set up, should pump about 45-50 gallons per hour, making it suitable as sole filtration for a tank of up to 10 gallons – which is another reason why they are so widely used in starter systems!  A large box filter can serve for a tank of up to 20-25 gallons.  For larger aquaria, several box filters may be used together, or box filters may be used in conjunction with other filter types to create total filtration that is adequate for the task.  For example, an outside power filter (which excels at mechanical filtration) can be used in a tank with a box filter loaded with coral gravel, which will provide chemical and biological filtration.

Don’t be misled by the simplicity, small size, or low cost of box filters!  Think of them as miniature canister filters and you will begin to understand their potential.  They are unmatched for versatile, cost-effective filtration.