The Ecosavr solar fish saves money by helping to prevent heat loss using a special liquid that sits on the surface of the pool virtually eliminating evaporation which is primary way pools lose their heat. This unique liquid is odorless, tasteless, non-toxic and 100% biodegradable so it’s safe for every pool and everyone. Just cut the top of package to activate the special dispensing design that will be effective for 1 month without you needing to check how much to add weekly, all you do is drop the fish in the pool and forget about it. For best results, use 2 fish for in-ground pools and 1 fish for above-ground pools. We recommend to use this product in the spring and fall or when the nighttime temperatures are cooler. That is when you pool loses the most heat!