Aeration and Misting Water
While we often hear of aeration being used to cool the water, you can find a more mild solution like using a water wand (fan spray) that lightly mists the surface of the water without generating the hard aeration normally used to increase pH. Do it in the late evening or early morning for best impact.
Using a pool cooler won't raise pH as quickly as aeration. To cool the water you want a fine spray of droplets shooting high in the air. Running it over night is very helpful, and running it during the day and parking yourself under the arc of the spray feels a lot cooler!
Finding a way to shade part of the pool from intense afternoon sun will help too. Shade Sails are fairly easy to install and will provide shade for the pool.
Realize that in Arizona and other areas that have high CH in the fill water, using accelerated evaporation to cool your pool water, also accelerates your calcium build up in your water.
Heat Pump Chiller Mode
Some heat pumps have a Chiller Mode to cool the pool water.
A Cheap Pool Cooler
This evaporator/aerator was put together with PVC pipe and is incredibly effective. A full sun pool will overheat without it and with it, you may have to shut it off from time to time because the water gets a little cool.
Remove one of the return eyeballs, and get the little plastic key that removes the inside collar that the eyeball screws into. Once that's out, a standard 1.5" threaded PVC fit directly into the return pipe. Glue some PVC pieces to make four "jets" to elevate the water then drill 1/8" holes in the top of each.
Threaded 1.5" out of the pool wall, Tee-d off 1.5" for about 2' both ways. Then 3/4" for the four "uprights" (I used four 1.5 x 1.5 x .75 reducing Tee's to connect) Capped off the uprights and drilled 1/4" hole in the top of each one.
No magic in that design...make it out of whatever you have. The four 1/4" holes seemed to work out pretty good as far as the height of the fountain. Stay fairly close to that total surface area (.78 sq. in) so you can elevate the water as much as possible. If it doesn't shoot high enough, cap off one of your returns....no harm done....your psi will go up quite a bit, tho.
The cooler works because of the evaporative process (which releases heat from the water) and will work beautifully with very hot temps. Opinion (not based on data) is that it is more effective during the day because of the lower relative humidity. In the Southwest, it would make icicles!
You can be in the pool and feel the cooler water dropping back to the surface. The higher you can elevate the water and the finest drops you can produce will give you the most effect. The volume of water you push into the air will have a lot of affect, too. A small, commercial fountain may work but doesn't produce much volume or elevation.
Quite cheap, incredibly effective and the kids think it's fun.
Polaris Socket Cooler
Build a simple one that plugs into the Polaris socket. This way you do not need to mess with the eyeball sockets, but the con is you have to run the booster pump for it to work.
Simple design, the most expensive part was the Polaris socket. You may have to tweak the size, number and position of the holes to make it work for the pool, hence the sleeves after the T.