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New Jersey Scuba Diving


New Jersey Scuba Diving

Aquarium Guide - Temperature

Aquarium Guide

Starfish with MusselTropical Aquaria

Tropical aquaria should generally be maintained at 75-80°F. In hot weather, temperatures up to 85°F are easily tolerated as long as adequate aeration is maintained. The addition of an air stone and a small air pump during these periods is helpful. At 90 F things start to get dangerous, and the tank should be cooled by floating ice packs or blocks of ice in it. Temperatures down to 70°F will generally do little harm, but the fish will be uncomfortable, and the temperature should be raised. Below 65°F is again dangerous for tropical fishes.

For freshwater tropical aquaria, a simple tube-type electrical heater should suffice for the winter. In the summer no heater is necessary, and typically your home air conditioning will keep the aquarium within acceptable temperatures during hot spells. Having bought a good heater, you should also get an inexpensive suction cup type mount for the free end. This will stand it away from the glass, and also prevent big fish from smashing it. It doesn't hurt to have a cheap spare heater for backup either.

Coldwater Aquaria


For local creatures, tolerable summer water temperatures range in the upper 60's to low 70's in the ocean, somewhat more variable in freshwater bodies. Coldwater aquaria should therefore be maintained no warmer than 75°F, preferably lower. Since winter water temperatures go right down to freezing, any temperature that does not form solid ice is acceptable in the winter. Extremely cold temperatures are not necessary in the winter, but their absence may throw off reproductive patterns that are keyed to the seasons.

In the winter maintaining an acceptable coldwater temperature range is not usually a problem, unless you keep your home unusually warm, but in the summer this can be difficult. If you have a consistently cool basement, then set up the tank there. Another alternative is put the tank in a small room with an air conditioner, but this can run up some very large electricity bills. The best solution is to use an aquarium chiller.

Aquarium ChillerAquarium ChillerAn aquarium chiller is a purpose-built cooling unit that directly cools the water in the aquarium. The two common types are in-line and in-tank. An in-line chiller resides outside the tank, and is plumbed into the external filter system, utilizing existing pumps and water hoses for circulation. An in-tank chiller places the cooling element inside the tank, connected to the rest of the unit outside by flexible coolant hoses. Both are thermostat controlled.

Most chillers are similar in design and operation to Freon-based air conditioners ( in fact, it is possible to convert an old air conditioner for this purpose. ) At the very smallest end of the range are a number of models that operate purely thermo-electrically. These have no Freon or moving parts, except for a single, easily replaced cooling fan, and are very quiet and energy-efficient. The size and type of chiller you will need will depend on the size of the aquarium and the expected temperature "draw-down".

For maximum efficiency when using a chiller, insulate everything you can - the bottom, back, and sides of the aquarium, any external filters, and especially all water hoses. Also, try to minimize external heat loads. Ultimately, all the power used by a water pump or filter is dissipated into the tank as heat. Therefore, a filter pump that draws 10 watts is equivalent to a 10 watt heater running all the time. There is not much you can do about this, except try not to use excessively large pumps. Another heat load is the lighting. If a light draws 30 watts and 1/3 of that is dissipated into the tank, that is again equal to a 10 watt heater. One way to decrease the heat load of a typical aquarium hood light is to cut ventilation holes in the back of the housing and in the top of the reflector, so that a cooling current of air can flow through the unit and draw away the heat. Most hoods already have cooling vents in the top, but these are useless if the unit is otherwise sealed. Other heat loads can include UV sterilizers and ozone generators.

Temperature Measurements

I now use only digital electronic thermometers. Radio Shack sells a simple model with a waterproof wired probe for $10-$15. It is accurate to +/- 1°F, and precise to +/- 0.1°F, which is useful for detecting trends in water temperature. The big display is readable from across the room, and the probe can easily be moved around to any desired location.

Temperature Changes

Striped AnemoneThe key to changing water temperature is to do it slowly, and in small steps. The main danger is in over-adjusting the temperature control and cooking or chilling the tank. Many small changes are safer than one big one. On a test-tube type heater with a knob control on the top, never make no more than a quarter turn at a time, without waiting 15-20 minutes for the system to stabilize. The fully submerged thermostat type heaters theoretically never need to be adjusted, as long as they hold their calibration.


Electrical blackouts can be lethal, as both the filter and heater/chiller will go out. If it is not possible to warm/cool the room by some other means, then cover the tank with a blanket. If the tank gets too warm/cool and you still have hot/cold water at the tap ( or ice ), try fashioning a hot/cold water bottle from a plastic bag and floating it in the tank, but don't just pour hot water into the tank. When necessary, ice can be floated directly in a freshwater aquarium, or in a plastic bag in a marine aquarium, to avoid diluting the tank with melt water.

Why Worry ?

Excessively high temperatures are dangerous to fish and other aquarium inhabitants because the oxygen levels in the water decrease with increased temperature, while at the same time the fish's oxygen requirements actually increase. A rule of thumb is that for any cold-blooded animal, the metabolic rate roughly doubles for every 10°C ( 18°F. ) Thus, a cold-blooded organism will require twice as much oxygen at 77°F as it would at 59°F, while at the same time, the available oxygen has dropped by approximately 20% ( likely more. ) Many aquatic creatures ( fishes especially ) are capable of greatly varying their respiration rate to adjust to a range of temperatures and oxygen levels.

Dissolved Oxygen



Saltwater 35deg

deg C deg F saturated
minimum healthy saturated
minimum healthy
0 32 14.6 mg/l 41% 11.7 mg/l 47%
5 41 12.8 mg/l 47% 10.4 mg/l 52%
10 50 11.3 mg/l 53% 9.3 mg/l 58%
15 59 10.1 mg/l 59% 8.5 mg/l 65%
20 68 9.1 mg/l 66% 7.8 mg/l 71%
25 77 8.2 mg/l 73% 7.1 mg/l 77%
30 86 7.5 mg/l 80% 6.5 mg/l 85%

Naked GobyLow temperatures are dangerous to tropical fish because they become more susceptible to shock, parasites, and disease. Much literature is devoted to the exact temperature at which each species should be maintained. This is bunk, most fish don't care that much, and the guidelines above are generally adequate. Most fish can also take a quick 2-3°F temperature change in stride, but not a lot more. Just think about how much control they have over their water temperature in the wild.

Aquarium Guide - Filtration & Aeration

Aquarium Guide

Hermit CrabThe main purpose of a filter is to circulate the water. This leads to better aeration and higher oxygen levels for both the fish and the critical bacteria which decompose the fish wastes. The more obvious aesthetic effect of filtration is the mechanical removal of particles in the water, but this is of much less importance. Since most aquaria are stocked far more heavily than natural conditions, constant effective filtration and circulation is essential. On large tanks ( 55 gallons or more ), consider using two smaller filters in place of one large one, and place them at opposite ends of the tank for maximum circulatory effect.

Filters should be cleaned only when the flow rate drops off noticeably. Depending on your setup. this may be only 2-3 times per year. Sludge should be rinsed out of the filter media with cool tap water, so as not to kill the beneficial bacteria. The filter media should then be reused as long as possible. Even charcoal can be reused several times before discarding.

In my experience, charcoal/carbon is far less useful than you are led to believe, and can actually be omitted. Most aquaria tend toward acidity, and this can be counteracted by the inclusion of some crushed coral, which is also inexpensive. This is especially useful with salt water. The special resins and other materials you can buy are probably useful to some extent, but for what they cost, I don't bother. Very coarse types of filter material are likewise not very effective. Old nylon stockings make excellent bags for particulate filter media.

Open cell foam is the best filter medium I know of, much better than glass wool. It can be purchased in sheets of 1/2 to 1 inch thickness at any fabric store, and cut to size with scissors. Several pieces of this thickness are easier to clean than one big piece, and will have a useful life of years. The fine grain of such foam works far better than the pre-cut foam pads you can buy at the pet store.

Aquarium FilterIn external power filters, there is a trade-off between quietness and convenience. The quietest filters I have ever used are the German-made Eheim canister types. They are dead silent when properly maintained, and very flexible and efficient. However, they are very expensive, and a real pain to setup, start, and clean. New models are much improved in these respects.

The alternative is the external type of filter that hangs from the back of the tank. These are reasonably quiet, self starting, and very easy to clean, often using disposable cartridges. There are many different brands, and quality varies. Models where the impeller shaft is fixed at both ends seem to vibrate less than models where it is fixed at one end only. Look inside the box before you buy. And I don't mean to imply that bio-wheel filters are not good, in fact it looks like an excellent principle. And a word about those disposable cartridges: you can rinse them out and reuse them until they fall apart! Not only will you save a few bucks, but you'll also preserve the beneficial bacteria.

I don't like air pumps for primary use. They invariably become noisy, even if they seem to be quiet when they are new, and the box said "quiet" in big letters all over it. Air bubbles are also noisy, and the actual oxygen transfer between the bubbles and the water is negligible. It is the water currents caused by the bubble stream that are beneficial to the tank. Air powered filters should be avoided, with one exception: air stones are quite effective for powering undergravel filters. The inexpensive diaphragm type air pumps also tend to wear out prematurely, especially in deep tanks where the water pressure is greater. Air stones also wear out.

Whatever kind of filter you choose, try to get one that will cause some turbulence and motion at the surface of the water in the aquarium. This need not be audible splashing, but it will help in aeration, and will also prevent the build up of oily surface films from food, etc. Bubbles from an air stone will also do the trick.

One more thing to think about is replacement parts. Inside any power filter is a little part ( called the "impeller" ) that spins 24 hours a day, 7 days a week, and it will wear out. The first indicator of wear is that the filter becomes noisy, and even begins to rattle. Some manufacturers provide replacement parts for these cases, and they are usually very easy to install. The result is that the filter will run like new, at a fraction of the cost of a new filter. Check to see that these parts are available before you buy. The same also applies to air pumps.

Undergravel FilterUndergravel Filtration

One of the best types of filtration you can get is with an undergravel filter. This is a plastic false bottom that goes into the tank underneath the gravel, and has one or more "lift tubes" that reach up to the top of the tank. These seem to have fallen out of vogue lately, as manufacturers are pushing those bio-wheel type filters, but the fact is that nothing is better than a good u/g.

An undergravel filter works by drawing oxygenated water through the gravel bed. This allows the beneficial bacteria to grow all through the gravel in much greater numbers, scrubbing the water like nothing else will. There is also a sort of inertial effect. It takes some time to build up the bacteria, but once they are there, you will not lose them like you do when you throw away a filter cartridge, and the whole system will be much more stable. The downside is that there is none of the mechanical filtration that I mentioned above - the particles will just keep circulating. Without some sort of auxiliary filter for this purpose, you will soon have a yucky looking but very healthy aquarium. The bacteria can survive for at least several days if the water flow is interrupted, and will also survive if the gravel is stirred up, but not too much. This can be a problem if you have big fish that are diggers. ( Yes, many fish like to dig , just like dogs. ) I simply would not set up a tank without an undergravel filter.

An undergravel filter can be either air driven, or you can use your power filter to drive it. To do this, block off all but one of the lift tube sockets and buy an extra long tube to fit the remaining socket, long enough to reach above the surface of the water. Then just put the intake ( or the return ) of the power filter into the lift tube, and you're done. You can also get a special 'power head' to drive a u/g filter, but in that case I would resort to an air pump first. Decorations can be attached directly to the u/g filter plate, but this requires some forethought, and makes it impossible to rearrange later.

I always set up a u/g filter in a saltwater tank using clean beach sand instead of gravel. First fill in the depressions in the filter plate with coarse crushed coral to get a smooth surface. Then cut a piece of 1/2 " open cell foam to fit tightly into the bottom of the tank and around the lift tube, and put it over the coral. Finally I added the sand. Conventional wisdom is that sand is too fine for such a setup to work, the water won't flow through it and the whole thing will clog. Wrong, it works beautifully, and I have had great success with this setup over the years. In fact, I believe the large area of flow-through coral is directly responsible for maintaining a healthy tank that requires little maintenance.

Protein Skimming

Periodic use of a protein skimmer can be beneficial in a marine aquarium. Protein skimming removes proteins, amino acids, and other chemical wastes that accumulate in the water. If a supply of natural seawater is easily available, then a periodic water change of 15-20% will do the same thing. Protein skimming is unnecessary in fresh water, in fact, it does not even work!

U/V Sterilizers and Ozone Generators

Ultraviolet sterilization of the water will kill harmful parasites and bacteria. The sterilizer is typically attached to the outflow hose of the filter. Since the ultraviolet bulb has a limited life, u/v sterilization should be used intermittently. Another use for u/v is to sterilize replacement water as it is added to the tank. Simply plumb it into the siphon.

Ozone generators are used to destroy water-borne parasites and bacteria. Unfortunately, ozone also has deleterious effects on just about every living creature in the aquarium.




I make no claim as to the accuracy, validity, or appropriateness of any information found in this website. I will not be responsible for the consequences of any action that is based upon information found here. Scuba diving is an adventure sport, and as always, you alone are responsible for your own safety and well being.

Copyright © 1996-2016 Rich Galiano
unless otherwise noted



since 2016-09-11