I'd like to help you out with your meter prob, but I never used one for PH I just use the liquid and small vial cheap and they work. No complicated either !! You reall should keep the res temps down below 72 . You don't want root rot or other nastythings starting down bwlow !! I did get a Hanna PPM meter it only cost about 30 bucks , that I use all the time..Good Luck alien8