I've been trying out the Heatsavr liquid pool cover for a couple of months now and must admit that it actually works pretty well. I have a 500sqft pool about 30 miles East of Los Angeles on top of a hill. Gets breezy and I've been losing about 1/2 to 3/4" per day to evaporation. Summer water temp in the mid 80's. Now I've been putting an ounce of the liquid per day in the pool manually, and have noticed a HUGE reduction in evaporation (albeit only minimal heat increase overall). I now am losing only 1/8 to 1/4" per day with a couple degrees increase in temp. Basically, I'm sold on the system. I can get 4 gallons on Amazon for about $250 shipped but the big problem is to automate the dosing. The Heatsavr people have a custom peristaltic pump injector that will dose the pool automatically, but it's about $300 and I'm cheap!
I'm going to attempt to build an injection system cheaper (seems easy!). I ordered a Chinese DC motor peristaltic pump on Ebay for $10 and will control it with a timed relay in my Jandy RS8 controller via a small 12v transformer. Now I need to get a check valve that I can screw into my pool return line and inject the Heatsavr thru it. For now, my question is: what kind of specs should I be looking for in a checkvalve? It will be feeding fluid (at low unknown pressure) from the peristaltic screwed into the return line to the pool (again unknown pressure). I've seen many cheap valves on Ebay but can any of you tech guys make a recommendation?