One thing I have doubts about switching from coldwater to coolwater or warmwater fish is: If the pond was prime for rainbow trout what makes you think the water is warm enough for fish that need warmer water to reach acceptable growth levels? Not trying to be negative just wondering if that has crossed your mind? I know you'd cut off the well but something doesn't add up here for me. Let me explain:

I'm surprised you were able to keep a 1/2 acre pond cool enough for trout with 20 gpm artesian flow and an addition of only 15 gpm well. 35 gpm just doesn't seem like enough, so either you have more flow than you realize, with the artesian and well, or you've got significant artesian flow coming in somewhere else. I know you're outflow doesn't seem to indicate that, but you may have underground outflow as well as inflow.

The reason I'm skeptical is my little 1/10th acre steep sided pond still climbed into the 60's in the summer with 10 more gpms than you were using (45 gpms).

Again please don't take my post the wrong way. Just trying to help.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.