When battling ich, hyposalinity is a great tool. The fish will adapt to the lower salinity, but invertebrates like Cryptocaryon irritans (aka saltwater ich), cannot. The proper specific gravity for the treatment is 1.010 (normal specific gravity is around 1.025 – 1.026). Be careful when dropping salinity though. If you drop it too fast, not even the fish will survive. Slowly drop the salinity over a few weeks time to be on the safe side.