Thanks foodchain. It is ambient heat right now but I live in hot temps so the water is currently 75 average. My system is 600 gallons. I plan to stock with 50 tilapia and then introduce a couple of catfish later for population control on the tilapia. So I figure I have room for a couple more fish that shouldnt hurt the system much. I was thinking maybe getting a fancy goldfish just for fun but I wonder if the tilapia or other fish would attack it. Any feeder goldfish I use now will probably get fed to my chickens when I get my tilapia.