I cannot say for sure without looking at you pH meter and probe, but the most likely problem is that you pH probe is broken or clogged. It probably needs to be replaced.i just got mine today and went to calibrate it, but only had a hole in the back no set screw? so i took the back off to find the adjustment on the board, but my problem was after calibrating it, i put the prob in my tank and it read 11.4 ph "oh no" now i know that's wrong, so i recalibrated and it still read 11.4. so i pulled out the old pinpoint ph monitor calibrated it put it in the tank and read 7.3ph then did a chemical test ya it''s 7.3 ??? now just so you know the prob that came with the milwakee arrived dry so i was thinking this might be a problem, but after reading some info thy say to soak it in a solution to activate it again but it still read 11.4, so just to see were the problem was i swapped the probes and the milwakee prob worked fine on the pinpoint and read 7.2 so i put the pinpoint prob on the milwakee sm122 and it read 7.2, so if any one can tell me what the heck (not what i really said) this kind of thing bugs the hell out of me.
Missing parts and bad probe? Can you send it back?