I'm so sorry to hear this, and sorry for you and for your dog. Heat stroke isn't pretty and can happen so quickly. I guess it would be troblesome to keep cleaned of algae but consider getting a couple of kid's wading pools and the dogs can get in an out as they want to cool themselves. I say get two because if you stack them it will help to prevent the dog's toenails from penetrating the plastic through both layers. Also consider a cooling fan if you can. I have one for my dog and though she is in the house she sure heads for it when she comes in aftrer getting hot running around in the yard. Home Depot stores have some sturdy black polypropolyene tubs that I think are for masonary work that make good cooling pools for dogs. I wish they were white but anything is better than nothing.
I once went to examine a dog that was found dead in a home in the middle of the winter. The dog was in a finished basement in a cage and the home was heated, but just regular temperature anyone might have in a home about 70*. The owner actually worked for me but was on vacation at the time and had a neighbor kid feeding the dog. There was snow on the ground outside, Feb. It was about two hours after death when I was contacted to check the dog and the body temp was just above 111* F!!! Amazing! It was a big dog but what could explain a temp that high 2 hrs after death, other than malignant hyperthermia? Just saying sometimes some weird things can happen.
It is 103* here right now and it feels really brutal! Again I'm very sorry for your loss.
Bill Knight D.V.M., retired
Hope you manage to hand in there. 
