W/C's and drop in SG

[Aquattro]

Originally Posted by bv_reefer

i already knew my SG, it's 1.023 and i just made my 5-gallon of w/c water at 1.023 SG, so now i can do actual water changes

so there we go. But you mentioned your RO water was 1.021 or something, which it certainly was not. So if your hydrometr said it was, you need a new one, or different RO water. RO is always going to be 1.000. Then you add salt to 1.025 (my preference) and then add to the tank. Take some water to the LFS to double check your readings.