Converting my tank to brackish water

[Larrimore]

Hello everyone, I've had my puffer for about 3 days and he's doing well. Eating snails and krill and housed with 4 ghost shrimp that have become mutual friends I suppose til he's bigger.
Anyway to the topic at hand. I purchased him from Walmart, so I started my tank as a freshwater. He is about 1.5" long, and I have him homed in a 20 Gallon marine land tank.
The help I am seeking is how to slowly raise the SG 1.002 a in a change, as in the correct calculation for how many gallons to remove with how many gallons to refill with the correct
amount of salt to balance the tank. I've been putting in a ton of time researching on my puffer and making sure I take care of his needs, but I dont want to leave the calculations to chance
so I figured I would ask for help to get a better idea.

Thanks everyone!

[RTR]

Water parameters? Ammonia, nitrite, nitrate, pH especially but give any others you have tests for.

[Pufferpunk]

Yes, how long has the tank been set up? If the system is stable it is OK to start raising the SG. If not, that is the most pertinent thing right now.

When you're ready: viewtopic.php?f=5&t=19348