I vote for more frequent smaller changes as well unless an issue arises that requires alot of water be moved out.
I also would stop adding tap water for top offs. You go to the trouble of getting real seawater so you might as well buy some ro
water from a lfs
or from a supermarket water machine for like 30 cents a gallon. It will for sure help your corals and water parameters.
+1 for not dosing anything you arent testing for. You especially, youre getting NSW
from the ocean so it will have everything you need. And if you do weekly pwcs you are replenishing any elements that are used up through out the week.