Review on 🐠 RZ Aquariums Salinity Refractometer: Accurate Dual-Scale Hydrometer for Marine Fish-Keeping, ATC Function, Saltwater Tester 0-100ppt & 1.000-1.070 Specific Gravity by Malik Munns

Originally bought a hydrometer how to install it in a salt water tank. Did some research and saw people claiming they are better for accuracy. You seem to be right about the accuracy. However, my underwater hydrometer lags behind by a mark or two. Anyway, now I have both and can double check the aquarium water with each. I don't have any coral yet, so as long as it's above the true mark, no higher. The higher the reading, the happier I am and the fish will be fine too. I've been into this hobby for a while now and don't worry too much about it, I know let the fish swim happily.