Tilapia froze to death last night.

[Ray Eklund]

So it is with great sadness that I lost my entire stock of Tilapia due to a power outage last night. I have a converted IBC with about fifty mature Tilapia. I have a huge amount of Beefstake tomato plants in the grow beds. The problem I have is my system is in my garage and in an enclosed insulated room I built about 6 ft wide by 8 ft deep by 12 ft tall. I have been thinking about going with a propane heater and this cinched it for me. One problem I have been dealing with that I hope somebody can help with is water temp/evaporation/mold...well obviously more than one problem. I have 3 200 watt tank heaters and with the ambient temp of around 70 degrees farinheit the water has stayed at about 65 degrees. I typically lose a third of my tank water in a month to two months time and with the evaporation the drywall is showing serious mold growth. Is there anything i can do to address these problems? Also, how long will the bacteria live in the tank without fish in it?