I agree with the refractometer, you can get them for a reasonable price on ebay (think I paid around $35 for mine). I was using a hydrometer at first and was getting VERY extreme readings even with multiple tests. I also agree that you should try only a few gallons at first. I had a salinity problem when setting up my tank (mostly due to the hydrometer I think). I took out saltwater and replaced with ro
and then it was too low. Start small!