This is what I did on my 750. I have a 2 gallon Lochnivar water heater with a 1500 watt element which is controlled by a digital controller I bought off of ebay for $40 that is used to control Kiln oven temps. It has a range of 0-999 degrees. Aquatic Eco sells external controllers for this purpose, I bought the components and built mine. My tank is in the garage and has seen 30 degree temps already and stays at 78 degrees which is what it is set at. Another thing I do is use a small 1500 watt space heater from Walmart that cost $15 to heat the air at the waters surface. I checked this morning here and outside temp was 45 degrees, water temp was 78 and air temp inside tank was 77 degrees. You loose most of your heat when the air temp is lower than your tank temp, this speeds evaporation causing the water temp to drop. If you float warm air across the surface you slow evaporation and the water will stay warmer with less wattage from your heaters.






Here are some pics, pump is a hayward sp1750 which is a 1/2 hp self priming. The pump runs 24/7 and in the pics you can see the ball valve going into the bottom of the drum, it is now throttled back to force water through the heater, hard to see but there is a tee just before the valve where a 3/4" line runs into the heater. Once out of heater it runs a separate line to the opposite end of tank. Just below the electrical box with the controller you can see the thermal coupling mounted into the pvc elbow. This was before I insulated it. In the last pic you can see the space heater. It is tied in with my exhaust fan the pulls air and moisture out of tank. This is on a timer where is runs for 2 1/2 hours then is off for 1 1/2 hours. So what happens is exhaust fan pulls out while heater blows warm air in. I do not run full on with the air only because of electricity. When it gets really cold I override the timer and let it blow warm air until the temp gets above mid 30s outside.
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