Since you have no life in the tank my suggestion would be to kill the return. Pull as much water as you can fit into a container (5 gallon buckets or larger can). Then add salt mix to the container to bring the SG up. Once it's up pump it back into the tank. Turn on the pump to let it circulate for an hour, then test and repeat if needed.
Got it?
This will keep salt from getting into the sand. Which is what would happen if you tried to mix in the tank
Got it?
This will keep salt from getting into the sand. Which is what would happen if you tried to mix in the tank