I Make RO
water ahead of time in a 30 gallon brute trash can. Then I put a powerhead, heater, and salt in the bin and let it mix for 24 hours. Ill Take out about 10-20 gallons depending on how long I've gone without a water change and throw the dirty water away and pump water from the trash can to the sump with a maxi-jet.
It's recommend 10% weekly for water changes, but you can find out what's best for your system..maybe 30% a month or whatever. Try to match the salinity of the new saltwater with the salinity of your tank water as close as possible.