salt, but you would do that in the form of salt and water
look at it this way...
plain water is 1.000, and as you add salt mix you start to raise the SG
, where the norm is the 1.025ish that people strive for.
The other thing to look at is, just because you have a 150g tank, your CC
and anything else you put in that tank is actually going to cut down on the liquid volume. So the more things you add, the less water you have for your salt that was to treat around 50g per bag and 150g for all 3
i.e. your 150g actually has 120(probably wrong) but enough salt for 150 gallons at a SG
of whatever your bag specified usually 1.025
anyone correct me if I am wrong, still new at this
One other note, while we are talking about salt...
When your water evaporates, dont mix the new water with salt, as the salt will stay in the water still in the tank. The only way I would add salt to water for top off is just to raise your SG
. You also dont want to have sharp increases in your SG
. To bad/stressful for the critters.