The untreated hydroton can cause a pH spike.
Are you pre-mixing your nutes? You don't use a reservoir in a soil grow unless you are doing a drip on a timer but even then you have to be 100% certain that your nutes are stable in the res. I've just recently worked on a grow where the pH problem was actually being exacerbated by a grower who pre-mixed her nutes in gallon jugs and over time the pH was dropping.
stinkyattic Reviewed by stinkyattic on . (pics)PH problem plants + form E-indoor E-soil E-2-4 gallon plasitic buckets CSL-Happyfrog, some has extra perlite, some with clay balls on bottom. all have clay balls on top to help maximize soil use. SCL-perlite. SCLR-slab ph, some are as high as 7.5 and others are around 7. E-tap water. E-7.6 ph (i now have a meter and i lower it to around 6.4. E-Age of plant, 1 month. E-botanicare, pure blend. veg cycle, 2-1.5-3 or something like that. Rating: 5