I'd start with verifying salinity. LFS salt water does not mix that high in Mg nor ALK, so I suspect salinity is higher than 1.026.
None of us calibrate as often as we should.
If that is not the issue, the next thing to check is nitrates & PO4 (checked by Hanna ULR). Low nutrient and high(er) ALK don't mix well for corals.
now im worried are top fin water testers good