Whatever the size of the marine aquarium, it represents a fair financial investment. That’s just the system comprised of aquarium and support devices. Then there’s the livestock, which again requires a sizeable financial outlay. It is necessary to protect the livestock in as many ways as possible, first because it is life and second because it is costly.
One way of protecting livestock is by correct husbandry, keeping the seawater quality high, correct feeding and the like. The initial way to achieve this protection is to invest in adequate hardware in the design stage obtaining properly sized powerheads, protein skimmer etc. An important part of this hardware is the heater.
Aquarium heaters nowadays are generally reliable and can be accurate to about + or – 1.5 deg F or better. The unit comprises a heater that is at the lower end of the unit and a thermostat that is at the upper end. The more powerful the heater, that is the higher the wattage, the longer the unit will be.
The heater is best fitted in a sump if there is one as it could look out of place in the display aquarium though in a reef they are usually fairly easy to disguise. If they are disguised then there should not be any interference with seawater flow around them. They should be clear of the sand and preferably fitted at an angle, not vertically, though with modern seawater currents this is not quite so important.
The size of the heater should be calculated according to the total net gallonage of the system. This can simply be achieved by checking the recommendations of the manufacturer. It is usual to also size to the room the aquarium is in – if a cold room more heat is needed than in a warm one.
The heater as said is generally reliable nowadays but, like any piece of equipment, they can fail. They could fail in either the ‘off’ or ‘on’ position. This is a major failure: if a protein skimmer fails then there isn’t a nearly immediate threat to the livestock, though of course it needs attention as soon as possible. A heater failure needs immediate attention not just when convenient.
Dependant on the air temperature, cooling seawater does become such a threat if the aquarist doesn’t notice the problem. Seawater generally cools fairly slowly, the speed based on volume and air temperature. Seawater that is gaining in temperature quite quickly is a more serious threat. This is because if the heater has stuck in the ‘on’ position heat is constantly supplied and the seawater temperature rises continuously, more quickly than it would cool. As the temperature increases so the oxygen content decreases. Further, there is a general upper tolerance level for corals and fish, above which losses will occur.
The potential problem can be guarded against quite easily. When the total wattage required to heat the seawater has been calculated, divide it by two and buy two heaters. So if 200 watts is needed obtain two heaters at 100 watts each. The heaters are set to the same temperature and fitted parallel to each other. Some aquarists put one at each end of the display tank, but if a sump is available they can go in there.
“200 watts is needed so if one fails the aquarium won’t be heated properly.” That’s correct, but the immediate danger is removed. If one heater fails in the ‘off’ position, then the other heater will apply heat and attempt to reach the design temperature. If it can’t reach this temperature it will not switch off. This means that the seawater will not cool down as rapidly and the heater will at least be able to maintain a lower temperature. This means the aquarist has considerably more time to notice the problem before there is real trouble. When a replacement heater is fitted all is well.
If one of the heaters sticks in the ‘on’ position then there will not be a danger of overheating the seawater with the problems that will bring. The heater that is permanently on will obviously continuously heat the seawater. The other heater which is operating normally will reach the design temperature and switch off. The seawater is now likely to cool down though more slowly than usual. When the temperature drops sufficiently the second heater will switch back on again and so forth.
Using two heaters doesn’t cost more in electricity: the wattage is the same as if there were only one. However, the livestock are protected from excess stress or even disaster.