Choosing an Aquarium Heater

Buying and Installing an Aquarium Heater
by 2manyfish - September 1999

Heaters are mandatory on tropical fish tanks unless you happen to live in the tropics. Except for a few notable exceptions (Goldfish, Koi, White Cloud Mountain Minnows, Lemon Barbs, Peppered Catfish, and a handful of others, which prefer cooler water), the majority of tropical fish prefer temperatures of at least 74 degrees and preferably a little higher.

Although hardy in most other respects, Livebearers such as Mollys, Platys and Guppys, really don't tolerate water much cooler than 77-78 degrees. Mollys and Platys in particular actually thrive in 80-82 degree water. Many disease and parasite problems common to Mollys can be eliminated simply by raising the water temperature to about 80-82 degrees. Some other fish that prefer water in the 80-82 degree range would include Betta splendens (Siamese fighting fish), Trichogaster leeri (Pearl Gouramis), Pterophyllum scalare (Angelfish), Epaizeorthynchus (Labeo) bicolor (Red-tailed Black Shark), Hemigrammus rhodostomus (Rummy-nosed Tetra), Metynnis argenteus (Silver Dollar), and Botia macracanthus (Clown Loach).

It is also important to remember that whatever temperature you choose, it should not fluctuate by much over 24 hours. If your aquarium room is warm by day and cool (or cold) by night, a smaller fish tank can experience wide temperature swings of 6 to 8 (or more!) degrees from the hottest part of the day to the coolest part (usually early morning). Although these temperature swings may remain within the limits of recommended temperatures for the fish, this can be very stressful to some tropical fish, and may account for some otherwise unexplainable mysterious fish deaths. It is preferable to not allow temperatures in a tank to vary by more than 1 or 2 degrees over a 24 hour period. Thus, if your room in which your aquarium resides is warm by day and your tank temperature would normally run, say, 78 degrees by late afternoon, then a heater should be used to maintain (at least) that temperature during the entire 24 hour cycle, including the coolest part of the night.

There are some important differences between brands and models of heaters. Almost every heater includes a little neon indicator light to show when it is working. The glass tube that is the main body of a heater is constructed of borosilicate glass, which resists heating and cooling without cracking better than ordinary glass. Cheaper low priced heaters generally use thinner glass walls in the tube. This makes them more fragile than heaters with thicker glass walls.

The electrical circuitry inside the heater is usually controlled by a bimetallic thermostat with a pair of electrical contacts mounted on the metal strips. Quality of these contacts is very important. Good heaters use German coin silver for their contacts. Silver contacts tend not to stick together, and make excellent and reliable electrical contacts. If you can find them, gold contacts are the best, but such heaters would be very expensive. Cheaper heaters may use unknown metals that may not function as reliably. To generate heat, all heaters use some arrangement of nichrome wire through which electricity is passed. The wire warms and the heat is transferred to the glass tube, and from there to the water. Better heaters use sturdier wire for longer lasting life.

Whichever heater you choose, it is wise to mount it close to fast flowing water (beside the filter outlet is a good choice), so water is constantly circulated over the heater. Some heaters come with little rubber or plastic suction cup devices to firmly secure the heater in position. This prevents the glass in the heater wall from accidentally striking the tank wall, which could potentially result in a fracture in the heater's glass, destroying it. If your heater did not come with such a mounting device, Lee sells heater mounting suction cups as an accessory item. Large fish (such as Oscars and Goldfish) can easily slam heaters around, so be sure to mount yours securely.

Heaters are rated by how many watts of electricity they consume. "Watt" is right for your tank? Well, a useful rule of thumb is to allow about 5 watts per gallon of water in an average room where the desired temperature of the tank is about equal to or less than 10 degrees warmer than the room. If you are attempting to run an aquarium at, say, 80 degrees while room temperatures dip to 50 or 55 degrees, then it might be better to increase that recommendation to 10 watts of heater per gallon of water. (Frankly, I have found the 5 watts per gallon rule to be extremely conservative. It would only be in an extreme situation where a larger heater would be required.) It is always a good idea to have a heater that is rated as adequate or slightly more than adequate, as compared to a marginally rated heater. A marginally rated heater may have to run constantly to barely maintain the desired temperature, and would have no reserve capacity should the room chill down a little lower than expected (such as when that furnace decides to fail on a cold winter morning). A heater with adequate capacity and a little reserve capacity will not have to cycle nearly as often to maintain the desired temperature, and will thus enjoy a longer service life. It will also be able to handle that rare and always unexpected demand for more heating capacity should room heat fail.

Some people recommend dividing the wattage between two heaters. For example, if you were running a 20 gallon tank and, using the 5 watts per gallon recommendation, decided you needed a 100 watt heater, some would recommend that you run two 50 watt heaters rather than a single 100 watt heater. They reason that in case one heater fails, the other would be able to pick up at least part of the slack and not let tank temperatures plunge too drastically before you could catch the error and you could secure a replacement heater. (People living in very cold climates should ALWAYS keep a spare heater or two on hand, just to handle potentially disastrous emergencies such as this.

A spare heater on the closet shelf is very cheap insurance if your tank full of expensive fish should suddenly be endangered by heater failure on some cold winter Sunday morning, when you might not be able to secure a replacement right away.) By dividing the heaters into two heaters, the reasoning continues, it also helps prevent the heart-breaking experience of a heater thermostat sticking in the "on" position, and thus cooking your fish. If you are in this hobby long enough, sooner or later you will either meet someone who has had that experience, or (heaven forbid) you might go through it yourself. Dividing the wattage between two heaters seems to make sense.

On the other hand, high-quality heaters made today (Ebo Jager, Rena Cal, others) enjoy very high quality construction with outstanding reputations for reliability and very low failure rates. I personally own a high quality heater (that, unfortunately, is no longer being manufactured) that has been in continuous service since 1962 and is still going strong 37 years later (as I write this in 1999). Paying a few dollars more for a heater may be all you need do to protect against unexpected disasters in your tank.

Some, such as the Heetmaster, are very easy to open and service, so you can inspect and clean (or replace!) electrical contacts or components if needed, something not every heater allows. Should you decide to attempt to clean your heater's electrical contacts, do so by gently swiping a piece of typing paper between the contacts. Never use an abrasive cleaner, and never use anything hard (like a file), which can severely damage electrical contacts. Exception: electronic supply stores sell a fine little instrument called a Relay Contact Cleaner. This is a smooth little band of metal mounted to a little handle, specifically designed for cleaning and polishing delicate electrical contacts. It is similar to a file, only with an extremely fine texture to it, almost the same as Bond Paper. It will not leave metal filings or other residue which later could cause electrical contacts to stick and the heater to remain stuck in the ON position. No submersible heater is easily opened and serviced, so it would probably be wise not to try. If you don't get the seal exactly right and water enters the heater, the heater will be ruined very quickly.

If you weren't already aware, NEVER put a heater in water unless it is unplugged and has been allowed to cool to room temperature first. The combination of hot glass in cold water can have spectacular and disastrous results. After placing the heater in the water, allow temperatures to stabilize for at least 5 or 10 minutes before plugging the heater in, also to prevent unnecessary glass breakage. Always inspect a heater for almost unnoticeable cracks in the glass before placing it in water. A hairline crack in the glass can result in catastrophic failure at a later date. Be very careful in handling the heater not to strike the glass against a hard object. Never clean a heater's glass with anything that might scratch the glass, which could cause it to fracture along the scratch line at a later date.

NEVER put your hand or arm in an aquarium with a heater plugged in. Should there be any electrical leakage, it could really ruin your day. Should your heater's electrical cord develop any hint of a cut or damage to the wire's insulation, play it safe and remove the heater from usage at once. Never attempt to repair the electrical cord by taping or by applying any insulating wrap - it's just not worth the risk to fish and fishkeeper. Either return the heater to the manufacturer for servicing and replacement of the wire, or discard the heater.

Most heater manufacturers picture their heaters mounted vertically on the tank. Of course, non-submersible heaters demand this mounting, and you CAN use a submersible heater this way. Used in this position, convection currents produced by warm water rising off the heater will tend to cause greater temperature shifts from one area of the tank to another. Without supplemental circulation, water on the right side of the tank will tend to be measurably cooler than water on the left side of the tank. There is also the problem of "layering," where warm water tends to rise to the top of the tank, leaving water at the bottom of the tank cooler.

However, you can take advantage of a submersible's slightly greater efficiency for heating (because no heat is wasted through the exposed assembly out of water column at the top of the tank if a heater is submerged), and also improve water circulation. Simply turn the submersible heater on its side, mounting it close to the bottom of the tank, like this:

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|~~~|~~~~~~~~~~~~ |
| |
| | |
| \========o |
^^^^^^^^^^^^^^^^^^^^^^^^^^

In this position, all the heat produced by the heater will go into the water column, and none directly into the air above the tank. (A glass cover will help to hold heat inside the tank where it belongs, and not allow it to escape into the air above the water. Evaporation is also reduced with a glass cover.) Water circulation will be improved in the tank because convection currents from the heater will gently stir up cold water from the bottom of the tank as warm water rises off the heater. You will see much more even heating in the tank by using a submersible heater in this manner. Another advantage comes at tank water changing time. If you have a vertically mounted heater and forget to unplug it, you can drain water down until the glass around the heater element is exposed to air. When you refill with water, it is possible to fracture the glass in the heater's tube. In my humble opinion, horizontal mounting is the preferred mounting for a submersible heater. Again, before mounting or moving any heater, first be sure the heater is unplugged. Remember, heaters operate from 115 volts (or 230 in Europe!), and your hands are wet. By unplugging the heater before handling, you eliminate any danger of electrocution or dangerous shock.

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Buying and Installing an Aquarium Heater by 2manyfish - September 1999

Buying and Installing an Aquarium Heater
by 2manyfish - September 1999