Ok, so using my DIY calibration fluid as described above, here are my new results.
The refractometer out of the box tested the 35ppt solution at 39ppt, it tested my tank at a salinity of 40ppt. After calibration with the DIY fluid my tank tested at ~36ppt (sg1.027). so that sounds ok, it was 4ppt high. Still higher than I would like but a lot less earth shattering than my original reading of 1.030.
I adjusted the solution as per the article for a hydrometer as well and found that it supports the newly calibrated readings from the refractometer. It gave me an adjusted reading of 1.0265 for the tank water
So it seems that the calibrated hydrometer supports the calibrated refractometer and I can be fairly confident that my refractometer is now accurately reading salinity right?
Sort of disappointing to find that a $65 piece of equipment billed as a must have for reefkeeping was less accurate out of the box than a $10 plastic instant ocean hydrometer.
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