My water temperature swings from 55 at night to 75 during the day on a hot afternoon. I assume the grow beds are the culprit. I live in central California. What can I do to keep my water temperature steady at night, while not causing it to excessively heat during the day. I have not tries simply applying a heater to the appropriate temperature for Tilapia yet.

I currently have goldfish and koi to cycle my system.