Depends on where you are. Being in Florida I dont worry too much about my tilapia. When the water cools down they lose their appetite. Tried once to provide a heated area, but that didnt work as well as I thought it might, so now they're pretty much on their own till the sun warms up the pool again.
BTW, gave up on F/D a couple years ago . Now doing iAVs style AP. Working out quite a bit better than my old F/D style.
I haven't kept tilapia, but I did keep 8 goldies in a 75 gallon tub. Water temperature is as important to the plants as it is the fish. I kept it outside in Virginia and the cool spring nights here really stunted my plants. I sold the system and dug a pond for the fish.