Aquarium Temperature – How To Control It

The aquarist has a responsibility in his/her aquarium to maintain stable water conditions, and this applies for fish only systems and also particularly for reef systems. The stability referred to here is the continuing maintenance of appropriate levels of pH, alkalinity, calcium and the like, and also the maintenance of appropriately low levels of phosphate and nitrate. What must also be included in water parameter stability is the [tag-tec]aquarium temperature[/tag-tec].

Temperature on the majority of wild reefs remains fairly constant all year. Tests of temperature on some wild reefs have shown variance. The following shows this:

  • Average temperature of all tested reefs: 82 Deg F
  • Average of reefs with lowest temperatures: 77 Deg F
  • Average of reefs with highest temperatures: 86 Deg F

So it would seem that if the temperature of the aquarium coral reef is kept between 77 and 86 Deg F then all should be well. This could be nearly correct. The corals (and fish etc) on the individual reefs have more than likely a tolerance for the temperature on those reefs and also any variation of temperature. This variation has been shown to be as much as between 15 Deg F and 21 Deg F *. These variations do not apply to the majority of reefs but do indicate that some reef’s temperature stability is not as constant as others.

A further and important point about temperature change on a wild reef is that it is slow. The reefs are washed by millions upon millions of gallons of seawater, and the seawater moving over the reefs is of course linked to the seas and oceans, with the colossal amount of seawater this represents. So increases and decreases in temperature are not going to happen quickly. As the system they live in is so stable and changes of temperature are so slow, the inhabitants of the reef are going to exhibit a tolerance to the changes.

Now look at our aquariums. A bit of difference to say the least! Even the aquarist who has a huge aquarium has less than a small thimbleful when compared to the wild reef. It could be said, with reference to seawater volume, that one fish in a home aquarium is one fish too many when compared to the overall gallonage available to reef fish. Of course, technology and knowledge of husbandry make the difference.

So corals are generally used to stability, though in some areas temperature may change significantly but slowly. In the home aquarium temperature, if permitted, will change quickly and by a large amount. During the day, the temperature may climb significantly as the aquarium seawater is influenced by summertime temperatures and/or by halide lighting etc. Then night arrives, the lights turn off, the air temperature falls, and the seawater temperature falls relatively quickly as there is only a small volume. This danger is more real the smaller the aquarium is. The nano reef aquarist has to be particularly on guard. All aquariums of whatever size are subject to the problem to a greater or lesser extent. So what to do about it?

The ‘usual’ temperature setting for a marine aquarium is 75, 77 or perhaps 79 Deg F, or somewhere in between. The corals and fish etc function at these temperatures without problem. However, the temperature increases and decreases generated in an aquarium can put reef inhabitants under stress. This stress will continue for so long as the aquarium temperature variations continue, and the greater the variation the greater the stress. This is not something the aquarist will wish his livestock to be subjected to.

If the temperature variation is more than 2 Deg F, in summer or winter, between the coolest point at night and the warmest point during the day, then the aquarist should raise the temperature setting of the heaters to 80 Deg F. This is a safe setting for corals and fish etc. This then means that the warming of the aquarium seawater by outside influences will take longer. When those influences are gone, the seawater will not have to cool down so far if it has heated up at all.

This does not mean that the [tag-ice]aquarium heater[/tag-ice] can simply be turned up. Doing so would be the opposite to what is being attempted. The heat level should be increased slowly, 1 Deg F each day as a maximum. It would probably be better to allow 48 hours or even more per degree of increase.

Nor does this mean that the need to monitor temperature variation can be abandoned. The aquarist in a cool zone may normally never see aquarium temperature climb above the norm, but may use halides. A day may come when the weather is particularly warm and then the rise could occur. In this unusual occurrence the use of a cooling fan may be all that is needed. Aquarists in warmer climates may always have temperatures over 80 Deg F. In this case the use of a seawater cooler (chiller) is the obvious option. There’ll not be any heating cost so cooling is a practical option. At an 80 Deg F cut-off setting the cooling device will work over shorter periods and thus cost less to run. The aquarist who has cool winters but warm summers may have no problem over the winter but may see excessive temperature rise in summer. If the excess is small, a degree or so, then fans may be able to cope. If the rise is greater, then a cooler may need to be used. Again, when the cooler is in use the heaters won’t be, helping to control running costs.

There is another good thing that can occur when the temperature setting is raised. Increased temperature increases the metabolism of the creatures of the reef. Provided adequate food is available, the tiny creatures on and in the reef (and DSB (deep sand bed) if there is one) will breed and multiply more rapidly. So there is more activity. Also, the fish will be more active (and hungry).

There is a danger. As the temperature increases the amount of dissolved oxygen decreases. However, in a properly designed and stocked aquarium there should not be a problem. In a poorly designed and/or badly overstocked system there could be. The great majority of aquarists I’m sure should have no fear, but just be aware.

As mentioned earlier, electricity costs could be affected. The aquarist who seldom sees a temperature rise above 80 Deg F will have the heaters switched on for longer periods. The aquarist will have to decide what the probability of excessive temperature variation is and act accordingly. The aquarist in a warm zone who sees temperatures above 80 Deg F may see an electricity saving. If the cooler cut-off temperature has been raised, the device will use less electricity. The aquarist who has cool winters and warm summers – winters will not make any difference, and if temperatures rise in summer then the heaters will switch off to be replaced perhaps by the running cost of a cooler. Hopefully, the cooler will not have to work too hard and costs may prove reasonable.

This simple method of achieving aquarium temperature stability, or at least increasing it, moves the aquarist nearer to the prize, all things being equal. The prize is a vibrant and healthy reef.

( * Source: Borneman E. H. Aquarium Corals.)