Question about salinity / refractometer

[irish mackerel]

I calibrated my refractometer using refracto juice to 35 ppt. Mixed my initial saltwater to 35 ppt and cycled my tank. Did a 20% water change today using natural seawater from my LFS here in south Florida. Checked salinity in the tank and it was 40 ppt. Checked the salinity of the saltwater I had leftover from the LFS and it was 40 ppt as well. Is my refractometer off? My understanding is that seawater should read 35.

Thanks for any help.

 

[Randy Holmes-Farley]

Maybe your refractometer shifted calibration, or maybe the fluid was off. Commercial fluids seem hit or miss.

If you have a scale, make your own.

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