Am thinking of buying one of these but would like to see some reviews if anyone has any links. I did splash out on a few of those disks but I don't think they work. I plopped one in the spa.....that's about 3 ft deep.....with the pump off. Then I measured the temp of the spa water and the pool water and there was no difference. It was sitting in the spa all day, didn't do anything. There were no disks in the pool at the time. Also I live in Houston, it was a hot day.