Keeping your Aquaponics warm

How is everyone doing at keeping their Aquaponics systems warm? We had to make some changes in our outdoor system and it is honestly struggling, since I cannot put a top on the fish tank. With my original home built design, I could place a styrofoam sheet over the top of the fish tank and it held most of the heat in there. I have the rest of the tank surrounded with those same sheets of 2 inch thick styrofoam. We have a very mild winter and I usually only have to cover the grow beds with sheets on nights we get frost. We had problems with low oxygen levels in the water and keeping the water flowing enough as part of the system that returned the water to the fish tank started to leak and get plugged. We needed a quick solution to stop loosing so much water so hubby created a bypass with a hose and pipe. It solved both of our immediate issues, but now my top will not sit snugly together. We only have goldfish & a catfish right now and they are doing ok in the cold water, but not eating or thriving. My system is on a patio with the tank under an awning, so a little protection from the elements but not much.