Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Get this size if you have an 18ft ring pool

I used this all summer long and it kept my pool water warm and clean. We got so much more use out of it. I bought one size smaller (this 15ft cover) and it fit nicely just inside the ring of my 18ft easy set ring pool. The directions said it should hang over the side but it worked perfectly with the way I had it set up. Save a few bucks and go for a size smaller than your pool. Trust me, it works and you will have a warm clean pool all summer long.* One warning, do not leave this on if you have an extended heat wave. At one point we left it on our pool and went on vacation for a week during 98+ degree weather. When we got back, the pool water was too hot to swim in - it was like a hot tub. I had to empty some out and refill with cold water from the hose.