Well it depends in part on the size (i.e. gallonage) of your pond... the more water,the better it will retain the heat, and smaller temperature fluctuations will occur between night and day. Even though it's been getting down to 50ish at night here, the pond temperature is holding at around 70-72F, with day time temperatures reaching low to mid 70s. You could put a thermal blanket cut to the shape and size of your pond (same as what is used in swimming pools) on the surface on cold nights and take it off during the warmer days. Two years ago, I pulled my Uruguayan cichlids out on Nov. 1st and the water temperature was about 35 F. Even a pleco, and they all survived and looked great. Amazing. You could also get an immersion heater (300 W, say) and use it on an "as needs " basis if you feel the water temperature is getting too low. Just some thoughts. I would experiment a bit. You might be surprised at how resilient these fish are. I'd be more concerned with temperatures that get too high (85F and up) since oxygen will deplete at higher water temperatures. Filtering the water and especially good, vigorous aeration is a must. And provide a shaded area. In Brazil, the fish wholesalers put palm tree fronds above the water along one end of their ponds to provide shade and security. Got access to palm tree fronds in your area of Florida? Good luck Casper. If you have any more questions, please feel free to ask.
Jim
