you need to add more salt to raise the salinity. A bad mixture when you do water changes could cause this as you may have not put enough salt to the freshwater mix.
Originally Posted by Sailfin Tang
If the salt reading is 1.020 what problems can this cause?
Also how fast can it be raised safely?
How did this happen? Is this a new tank? Do you check your salt mix before you add it? Do you let it mix with a strong powerhead for at least 24-48hrs before you add it? A reading of 1.020 can be quite disastrous in a reef tank. Most reef inhabitants need a reading of 1.026. Don't raise it more than 1.002 per day and it needs to be dribbled in. Please explain how it got that low. If it was FOWLR it wouldn't matter that much but reefs are very sensitive.
Just use saltwater (mixed at the level you want) for your top-offs and when you get it to the level you want, then go back to using RO for top-off. This is a slow safe way to raise SG.
First double check your testing equipment and clean it. If you are low, then start raising it with saltwater top-offs.