I have a FOWLR and an APEX EL. The PH probe that came with does not calibrate. I do manual Ph checks time to time, the PH probe is just for checking the trends. As replacement probe, I looked at BRS, Neptune probes and someone in R2R said Pinpoint is good so I bought that. While I was searching I noticed a bunch of AlibabaExpress lab grade probes. The prices are about $8-10 and the shortfalls are long shipping times and short cable lengths. I can order one and check it out, but anyone tried them?