The cheapest and most effective way of heating a large predatory catfish pond?

[Muckfish]

Not sure if it helps but we had a low of 40f last weekend. My tinfoil barbs and pacu were feeding and well today. I do make sure to kill the aerator and have the deep well flowing. I need to get out there in the dead of night and get a temperature reading. Have a low in the high 30s coming up I guess that will be the real test. Jewel cichlids also doing well.

This is a natural pond no liner.

 

[Fishman Dave]

Would be very interested to know the water temp at depth with the well flowing. Occasional drops in air temp to 30f don’t really tell us enough since we all live in different areas and our ponds react differently.
If that was where I am a drop to 30f overnight and my outside pond even at depth of 6ft would be 35 max as usual day temp would be 40 max.
Even at 20c or roughly 68f my indoor pond seems cold and the fish all start to go into hybernate mode and feeding really slows. Can really see a difference when a hot water water change brings it back up towards 25. But your longer term lows with less rapid fluctuations may be “better” for the fish than my cyclic monthly up to 25 over a few days, drop to 19 in a week spend 3 week at 19 then back up to 25. (For five months of the year).

 

[andyroo]

FYI/Note to above: aforementioned 800W heater is installed with an old wave-maker strapped to the side.
Keeping a nice constant 22C through nights of 18~20, including rainy nights of at 19C. Days are 24~6 right now if sunny, rainy/foggy stays ~22.
Now let's see what the power-bill looks like...

 

[Muckfish]

So as of this evening I left my digital temperature prob outside. It read 50f at 7:40pm this matched the weather channels temp to my location. So I went to the pond and got a reading of 68f in the shallows and to 3 feet. The actual water flowing from the well that travel 8’ then drops as a waterfall was measured at 79.8. So I would have to assume a deep well will have a warming effect on a pond and even more profound if the pond is smaller. I’m not sure if I’ll make it out early enough to test at the low of 36 but maybe this will help someone. I’ll update with the pacu and barbs condition following our low of 36f tonight.

 

[Muckfish]

Had a low of 30f with frost on the ground. Haven’t seen the pacu at all. Sucked it up and went for a swim. All 13 tinfoil barbs alive and well and I found the pacu alive and well but mostly inactive and no interest in feeding. The barbs feed lightly. This is my first year with pacu outdoors and I was worried about the winter. Glad to know I can keep them alive and kicking during the winters (so far). I have 11 more I am growing in my garage but am going to wait a little longer before releasing them to the pond. So the well was like 2500.00 so I’m going to guess this may be the cheapest way if you’re pond is of size to receive a constant flow from such a well. I believe it’s around 40-60 gallons per minute.