So I just re calibrated a cheapo PH pen after less than one flower cycle and had a difference of over 1 point. Nice to know I've been sabotaging myself, at least I can avoid it in the future!
This is a very cheap meter from amazon so I imagine its fairly low quality but unless your shelling out the big bucks for one of those real nice PH probes this is probably similiar to what alot of other people might use, so be aware that they will swing out of calibration quickly. I'll probably start re calibrating this one bi weekly. Anyone have suggestions for more reliable meters that won't break the bank?