Reporting back on what I've observed so far with this setup. On 90 to 95 degree days the water temp consistently gets up around 86 degrees during the day, and remains around 78 to 80 degrees at night. However, we had quiet a few days where the temp topped 105 degrees, yet the highest water temp I ever observed was 88 degrees. The only fish I have in it still are 3 tiny fry I took locally that was in a wash area that would soon dry up. They were so tiny I'm still not sure exactly what they are, but are Cyprinidae and probably Notropis. After they grew a bit the line down their side is fairly distinct. They are growing fairly well even though they've never been fed. They have done well through the hottest part of the summer. The setup hasn't changed since the pics I posted, and no circulation pump or waterfall has been added to date.
These water temps put significant, but not too extreme, limits on what I can consider keeping in it. The temps actually fair better than standard aquariums under the same condition. I basically have the information I need to consider inhabitants now. The pool also has a few pond snails, which has done well and have raised some young. These snails have always died in my standard tanks, even when kept in the air conditioned main house where I rarely go. The water remains completely clear of any algae, with the exception that some of the rocks on bottom maintain a splotchy green tint with no meaningful thickness.
I did have one Gray tree frog come inside to the pool and sing at night for about a week just prior to the 105 degree temp spikes during the day. That was the only one to take interest in my inside pool, though quiet a few (various kinds) sing at the outside pool near my front door that is essentially the same size.
In the past week I have also had a toad frog that comes in my front door every night and hunts around my foot stool. We've recently had a large cricket explosion and they come in and run around on my floor. This toad has figured out that these crickets are much easier to catch on an open floor. It knows the way to the front door and except for last night hops out every morning shortly after daylight. Last night it decided to spend the day under my chair. It has become so fat that it can no longer stalk its prey like it did when it first came in. When it hops it rolls forward when it lands because its belly hits first. It's eyeballing me as I type this