what should my nect step be?
So stop dosing the aquavitro eight.four. You need to let your corals slowly take up the excess alkalinity and calcium, and like Uncle99 said reduce your water changes to 10% weekly which will help bring your alkalinity and calcium back in line. Slow is the name of the game in reefing and when you think you are doing things slowly slow down even more.
Testing your saltwater before you do waterchanges is a must. If it has really high alkalinity and calcium levels than it isn’t helping to change water. If you need to switch to a salt that has much lower levels of alkalinity and calcium then that will help you tremendously. (Red Sea in the blue bucket, has much lower levels than your tank currently does as an example). I also wouldn’t be overly concerned with the NO3 levels and I would closely watch the PO4 levels and bring them slowly down, doing it too fast with GFO will do bad things to your corals. So be careful .