Well, public water varies from one town to another. Chlorine isn't good for plants, & the other chems in public water vary according to the water quality, so who knows what's in there that may react with other chems. I'm very lucky to live in the country & have spring water. pH is a very touchy thing, maybe some chem in the water is causing a reaction which in turn causes rebound in the pH after you have adjusted. It couldn't hurt to change to the recommend distilled water as recommended. I once worked in a pet store as fish dept mgr. The public water in that town was so full of chemicals we couldn't use it for our fish even after I de-chlorinated it. Couldnt even make coffee with it, so even should the water turn out not to be the problem, I'd still change it to distilled. I haven't done hydroponics in a few years, & chems, nutes etc has probably changed a lot since then, but I think it's a good chance changing the water will make a difference. Try that, & hopefully one of the guys who are up to date on hydro will jump in & tweek/add to the info I've given you. I always found hydro too expensive to maintain. I'll poke around & see if I can find a thread on hydro that might help you more.~~~~~~PEACE!~~~~~~~