The 38 salinity is basically an SG of 1.029. 36 is basically 1.027. Most reef tanks are set at 1.026. which corresponds to a salinity of 35.2x2x4 isnt 75g its 120g. 38 salinity is high looking for max 36 most go by sg not ppt but some do. Ie 1.025sg or 1.023 or whatever 1.026 and 36ppt are about the same and like I said the highest it should be.