Do you let your water sit out for a day or so before you ph it? Cause If you don't that will probably help your problem alot. It gives the chlorine a chance to evaporate. So let it sit out in your grow room for a day; nute it and then ph the water. The ph tends to gradually rise in hydro systems which is ok because particular nutes can only be absorbed at particular ph's so a slow rise in your ph from 5.5 to maybe 6.5 after about 5-7 days is good. But 5.6 to 7.1 in one day is definitely not what you're lookin for lol.