I can't keep my PH stable. It seems to be changing about every 36 hrs. I have one of those liquid test kits. Ill check the water, it'l be green ,about 7.0. Ill add some PH down, check it about 20 mins later, yellow about 6.0. The next morning it'l be ok, but when I check it in the middle of the day, about 36 hours since the first check, it'l be green again. Could this be caused from TAP water?