Yep, you'll just measure how much it takes the first time you mix your water to your ideal parameters.
Then be sure you use RO/DI for top-offs, just like with reef tanks.
When doing water changes, you remineralize to match your tank parameters.
You may want to pick up a $10-$12 TDS meter on eBay so you can more easily keep an eye on hardness shifts. Many shrimp keepers use them to keep an eye on when water changes are needed.