This is the second season we've used the solar fish. In my experience, in Central Texas, it warms the water 6-8 degrees in a matter of several sunny days. Before we got the fish, our pool would lose heat at night, and every morning was like starting over at square one temperature wise. The fish kept the temperature from dropping back down and allowed it to keep climbing even higher the next day. I have young children who have a higher tolerance for cool water than I do :-). There is no way I wanted to mess with a cover when the kids would get in and out of the pool several times a day for 20 minutes or so. It extended our swim time both in the Spring and in the Fall. I noticed absolutely no oily residue or coloring/clouding of the water. I do not think it is as finicky about water motion as some other posts mentioned. We used the filter as usual and as stated before were in and out of the pool often. I w ould suggest you try it for $10 and see if it works for you too!