Sorry, skipped to here after I read you're not interested in solar panels, which is what I was going to suggest. Wouldn't panels for cooling and heating pay for itself in the amount of gas you pay for in the fringe seasons? Anywho...
Have you considered shade sails? I see you mentioned umbrellas, but you could cover most if not all of your pool with shade sails, they don't have to be dragged around and they are "wind proof." They look cool, too. They're relatively easy to take down (when you don't need them). The other benefit is that I really enjoy having a place to hide from the sun, even while in the pool. Shade sails could cover both some portion of your pool and some portion of your deck.
I'm not sure exactly what heats a pool, how much is air temp vs sun exposure. I see someone was talking about dew point. But keeping sun off your pool bottom certain should help.
First, our gas is ridiculously cheap here, I pay $0.29 per CCF, which is about 25% the price of gas in California. Also, while solar heating would be nice for early season startup and might help to cool the pool in the evening, I'm not sure it's a cure all. I'd rather save the money and just use it for gas and heat as needed. For cooling, I'd rather spend on a Glacier than solar, but given the pool temperatures I've been able to maintain/average, I don't think a Glacier is that worthwhile, but I'll make that determination at the end of September.
Shade sails is something I have considered multiple times. I do have a few challenges just with the topography. I actually bought a huge shade sail, and I have used it for parts of my deck, but it is a lot of work to put up and take down. Originally, while the pool was under construction, I considered trying to put a shade sail from my main deck and attach it somewhere on the other side of the pool, however, there's nothing to attach it to. I'd have to put a large and very tall pole on the corners of my pool, it would quite disruptive to the view line. I may give it another go, trying to tie into the metal railing round the fountain bowls, however, it's a multi-person job. Also, I underestimated the amount of time it takes to get everything ready to go into the pool, I'm trying to minimize more things. Regrettably, between just getting dressed and sun block, I've got a ton of steps before going into the pool: Remove patio furniture covers, remove outdoor tv cover, lower four coolaroo shades, tie shades into each other and into the mounting hardware, uncover and ratchet up three umbrellas that are taken out of storage. It's a 10 minute ordeal and similar ordeal to clean up at the end of the night, the shade sail would add quite a bit more.
Anyways, 88-89 is the perfect temp for us, and we're able to pretty closely maintain that, so I'm pleasantly pleased and surprised.
Cheers!