Refurbishing A Severely Neglected 4000 Gallon Pond

[BlackDog]

I suspect you will find the waterfall warms the water, rather than cooling it, at least during daylight hours. The atomization of the water as it splashes on sun-warmed rocks will likely heat the water. If you provide a shady refuge for the trout by planting trees or shrubs to block the sun, they may be able to tolerate the heat. In any case it is a neat project and I hope it works out great for you.