I am new to the saltwater world. I have always wanted to take it on but was too intimidated. Recently I have purchased a 75 gallon tank and have just went for it. I mixed my own saltwater using Instant Ocean. Since doing this I have checked my salinity in the tank with the hydrometer that I purchased but I am getting different readings just about every time. Sometimes too high, other times too low. I’m checking from different water depths also. I have a flu al canister filter going, today is Day 4.