First I was not sure about these solar rings because of 50/50 reviews but i wanted to give them a try. I have a 16000gallon inground pool 400sq...I ordered 13 of these and covered 90 percent of the surface. And i also ordered hooks and put four hooks on my side yard so i can store them while not using. After one week my pool water temp up about 10 degrees and before i was losing 5 degrees overnight and after the rings now i am losing 2 degrees a night. I am also using liquid pool cover too in addition to solar rings. Now my pool water is about 85 and wife is happy!!! I am cleaning these ones a week with a garden hose.... It is not very easy to use but pool cover is way worse.... What i got is the latest model so be careful with what you order....one last note is we had two days of winds gusts up to 35miles per hour and they stayed where they are :) i recommend it if you don't want to spend your money on a heater....