Drop a thermometer into the pond below the surface. My thermometer is in the veggie
filter right where the water comes in, pump is 1/2 way down the 4' depth.
The veggie filter plants did fab while we were gone for 3 weeks. Took the dogs with
us (van camping and staying with relatives). Hired somebody to come in every 2 days
feed the birds, feed the koi, check the pump and air was going fine, the air
conditioning was on inside. The water was down a bit when we got back, but also
crystal clear. The veggie filter plants were going gangbusters. ^Yes, it was
helliously hot here in Milwaukee but we do have shade up over the pond.
BTW, we went on vacation to Cape Cod... mid to upper 70's the whole time. The Rvan
is air conditioned when we just plug it in.
Somewhere between zone 5 and 6 tucked along the shore of Lake Michigan
on the council grounds of the Fox, Mascouten, Potawatomi, and Winnebago