In this case we’re not considering action where the aquarist has found an ammonia or nitrite reading, but suitable action when the seawater has overheated or is too cool.
Overheating could be caused by a rise in the temperature of the air surrounding the aquarium which is maybe made worse by metal halide lighting. This is most likely in the summer months. The heaters function correctly and turn off when the design temperature is reached, but the seawater continues to get warmer. This can be dangerous to corals which can tolerate very high temperatures for only a fairly short period, and to fish because of oxygen reduction. If there are many fish in the aquarium demanding oxygen in addition to the oxygen hungry bacteria in the bio-filter then trouble or even disaster might not be far away. Cold seawater holds more oxygen than warm and as the temperature rises so the oxygen continues to reduce.
Most aquarists are aware of their probable summer weather and take care to be prepared. Some arrange fans to blow across the seawater surface and these could be controlled by a sensing device. The movement of air created serves two purposes, first warm air generated by the lighting system is countered and secondly the seawater temperature rise is controlled or at least reduced. In an area where a temperature rise is regular the aquarist could have invested in a more effective cooling device called a chiller. The chiller’s temperature control is set 2 deg F above the design temperature, meaning that the heaters will have turned off before the chiller activates. These two methods, fans and a chiller, used together or separately, should be sufficient to deal with any seawater temperature increase except perhaps one.
The possible exception is where the heater/stat sticks in the ‘on’ position. If the aquarist has followed the recommended route and installed two heater/stats, each rated at one half the heating requirement of the system, then the trouble should be reduced – in this case when the design temperature is reached one heater/stat will turn off leaving one on. The temperature rise will therefore be slowed and the cooling system(s) in place will slow the increase further. Hopefully, the temperature increase will cease at the point where heat loss equals heat being applied. The aquarist should notice the problem before any real damage is done.
What if the aquarist is using one heater/stat rated at the full heating requirement for the system. If it sticks in the ‘on’ position the heat being applied is double that in the previous paragraph and the temperature rise will be more rapid. Any cooling devices will have an effect on the rise but it will still be more rapid. If a chiller is employed, can the chiller, in direct opposition to the heater, control the temperature?
Sometimes seawater heats up only once or so and it is not worthwhile obtaining a chiller. Usually a fan is sufficient but the aquarist finds that the seawater is quite a lot warmer than it should be, maybe because of a particularly hot day. There isn’t a problem with the heater/stats, they have turned off.
The first thing is to turn off the lights over the aquarium if they are capable of putting heat into the seawater, and this applies particularly to metal halides. Corals will not suffer from one short day. Next the seawater temperature should be reduced and there are ways of achieving this. There isn’t any need to turn off a properly functioning heater/stat of course. The first possibility is to place plastic bags filled with ice in the seawater preferably in an area of good circulation (watch out for displacement), this could be in the sump if there is one and it is practical. These cool ice bags should be kept away from livestock. The ice will of course melt and if necessary the bags can be refilled.
Another possibility if it is practical is to run the return tube from an external filter through a bucket of cold water. This could mean temporarily extending the tube. The seawater flowing through the tube will be cooled by the cold water. The seawater could need to circulate through the cold water many times before it is sufficiently cooled, and a check will need to be made periodically to ensure the water in the bucket remains cold.
The advantages with these emergency cooling systems are that first they’re effective and second the seawater doesn’t cool too rapidly which in itself could cause problems.
What if the seawater is too cool? This could happen because of a power cut or because a heater has failed.
The first option, probably not the best, is to obtain a glass pan or other seawater safe utensil suitable to have heat applied to it, and fill it with aquarium seawater. This is then carefully heated on the oven to a temperature higher than usual but well below boiling. The heated seawater is then returned to the aquarium. There is a problem with this – if there is a power cut the circulation system will have stopped. So, at the same time as the heated seawater is being returned to the aquarium, the aquarist will need to stir the seawater with a clean suitable utensil to try and mix it reasonably. Another way is to copy the ice bag system for cooling the seawater. This time, obtain screw top glass bottles and fill them with hot fresh water (watch out for bottle glass cracking and seawater displacement). Leave enough air in the bottles to allow them to float. Refill with heated fresh water once they cool down. In this case as well the aquarist will need to stir the seawater in an attempt to spread the heat.
If the seawater is found to have cooled because of a power cut, once raising the temperature has been achieved the aquarist could lay blankets across the aquarium to reduce heat loss, though a periodic check of temperature will be required.
Having a battery operated powerhead would be an advantage for moving warmed seawater in the event of a power cut. Some aquarists have battery back-up for the essential parts of their system, such as circulation and heating.
If there has been a heater/stat failure, then once the aquarist has cooled (or heated) the seawater sufficiently there will hopefully be time to obtain a replacement as seawater cools naturally slowly, subject to the air temperature surrounding the aquarium.