27th July 2012
At the time of writing the UK is going through a period of very warm weather so it’s a good time to remind you about the danger that overheating can present to your reef tank. At this time of year reef aquaria can often reach potentially dangerous temperatures, bringing with it two distinct problems: heat induced coral bleaching and depleted oxygen levels.
Saltwater has a lower capacity for carrying dissolved oxygen than freshwater, as temperatures increase this carrying capacity reduces, in a reef with poor gas exchange the level of oxygen in the water can easily drop low enough for animals such as fishes and mobile invertebrates to asphyxiate.
I’d suggest checking that all pumps are working properly and efficiently and making provision for increasing your water movement in case of a prolonged period of hot weather. Making sure that the surface of the water is sufficiently agitated will both enhance gas exchange and aid temperature control via evaporative cooling. I’m currently recommending around a centimetre of “wave height” on the surface of the water, you’ll find that this will also enhance the effect of glitter lines, especially in an aquarium lit with fluorescent lamps.
Although you can mitigate the effects of high temperature induced oxygen depletion by increasing gas exchange, this will only go part way to helping corals to survive. This additional water movement can greatly enhance your corals chances of survival at higher temperatures and may be all that’s needed in some reefs, but ultimately you need to control the upper temperature reached in your aquarium.
It’s unfortunate that the cost of cooling a reef can often be as great, if not greater, than the cost of lighting it. Some reefs may need some form of cooling for the best part of the year owing to the way they’re lit. Your choice of methods of temperature control includes: refrigerant based chillers, evaporative cooling chillers, fans, air conditioners, and extractor fans.
Refrigerant based chillers and evaporative cooling chillers are the most expensive options.
Air conditioners are also expensive but they do have the bonus of controlling room temperature, which you and your family may well appreciate (it may also be a selling point to ”the significant other”, who may well have objected to the purchase of that expensive aquarium chiller!).
Extractor fans are useful to a degree but may make little difference once the room temperature is the same as outside.
Fans can be usefully employed to blow along the surface of the water to promote evaporative cooling, they’re cheap but do remember to take care in their placement as the last thing you want is a mains fan ending up in the aquarium! If possible choose a low voltage fan for safety.
Fans can also be extremely useful with enclosed aquariums and may improve how the tank runs on a daily basis, rather than just at times of high temperature, by improving gas exchange at the surface.
Don’t be tempted to turn aquarium heaters down or off as this will have no influence on water temperature during a warm period, indeed it can be detrimental to your reef when normal temperatures resume if you forget to turn them back on; if you see that a heater is turning on when your tank is running at an elevated temperature it is faulty and needs to be replaced.