I use a regularly calibrated Vertex refractometer.
I actually tested my top up water and it was 0 on the same refractometer.
To clarify, the Dino and Cyano happened due to the salinity increase, and now, after 3 30 gallon water changes (it's a 95 gallon tank with 60 gallon sump) we're back to 1.24-1.25 and the dino's are all gone with very little cyano in some lower flow spots remaining.
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