You replace any evaporated water with RO
water. Use saltwater for water changes. Just keep an eye on the salinity, you don't want to change salinity too quickly.
It looks like you inherited a pretty good reef setup. Only suggestion from looking at your list is the canister filter. With 28lbs LR
you would do good to only run carbon in the filter, you may already be doing this? Otherwise, it sounds like my tank