I have an Intex oval 12' x 20' x 42"

It holds about 5000 gallons, and so I plan on running the pump 4 hours daily. Pump is connected and has run once. I haven't put anything in it except water. I tested for pH, and it seemed to say that pH was 6.8 or below, but I'm not sure if I did the test right. I filled with water to the top two windows (or top dark line between them) then added 5 drops of red pH. I read that low pH can damage the liner, so I need to know what to do to bring it up, but I also wanted to be sure that I did the test correctly.