Estimation on how cold will my pond get - intent is to know if certain fish can survive in it
I doubt a pond temperature will stay above 60 in central FL winter.Without circulation there will be large temperature gradients caused by stratification, especially on warm days. Surface plants probably lower the maximum temperatures. For such a large pond ,the relative humidity and wind will make a temperature difference ( evaporation is a major heat loss).  As a comparison , I have a small ( 1000 gal) pond with circulation and although our air temperatures are usually 98 -day and 76-night, I have never measured a temperature over 83 F and usually lower. So the water temperature is definitely lower than the average air temperature in summer. In winter I protect my pond from low temperatures but it gets to 52 F . However, tropical fish like danios, swordtails and mollies survive that temperature in pond conditions , although books will say such temperature will kill them . What fish do you plan to have ? With the history that FL has for raising tropical fish , I would think there would be information available , such as from the FL Dept of Agriculture.