Southwest Aquaponics and Fish Hatchery, an aquaponics vendor and tilapia farm located in Glendale, AZ, recommends winterizing your aquaponics system using heaters along with and heat pumps:
Recommendations from Aquaponics 101, at the following link: http://synaptoman.wordpress.com/2009/05/31/aquaponics-101-the-challenges-of-winter/, are as follows:
Heating is thus the only option if you want to raise Tilapia in your aquaponic system. Your choices here are either solar or electrical heating. Solar is great but, is only of use during daylight hours. Electricity is expensive, especially considering that Tilapia is not considered a high value species. There is also the option of heating the water with a boiler, burning wood, diesel or gas, but this is probably only an option for larger commercial systems.
You must also bear in mind that your grow beds are like massive radiators and absorb heat during the day from the sun, but at night rapidly lose this heat to the environment, thus cooling the system. If you have a heat pump connected to your system, you’d obviously like to set your timers to run more at night to heat the water, but this also means that the water will also run through the grow beds and lose more heat than normal. Catch 22.
It’s not really a “pump” at all as you need to pump water through it to work. It operates identically to an air-conditioner, but in reverse. What it does is extract heat from the air around it and transfer it, by heat exchange and compression, to the water flowing through it. The colder the ambient temperature, the less “heat” there is to extract so the harder it works and the less efficient it is. We normally try and achieve a heating capacity of 10 deg over ambient. So if the temperature plunges to 5 deg, you can’t really expect the heat pump to give you more that 15 deg out.
Fortunately, water heats and cools quite slowly, so an overnight drop to 5 deg doesn’t mean that your system temperatures will drop to 15 deg as it takes some time to drop.
Two survival tips here, are firstly to provide as much insulation as possible. Enclose your tanks in a greenhouse, insulate the floor and walls of the tank and cover them at night to retain the heat. The second tip is to, if possible, reduce the volume of water to be heated. This could be achieved by dropping the water levels in your ponds and sump for the duration of Winter, or maybe even reducing the number of ponds to be heated. I use a combination of both strategies in both my home and commercial systems.
If you intend breeding Tilapia through Winter additional heating (normally with an element) is required as well as supplementary lighting. If you provide Tilapia with 26 deg temperature and 18 hours of light per day, they will spawn year round.