I would have held off on adding any corals. The tank is too new. Not sure how they’ll hold up to those parameter swings.
How did you cycle the tank?
Do you have plenty of bio media in the sump?
On my latest build I added coralline algae in a bottle very early on. Of course it takes months to show up but it contributes to the maturation process
https://www.algaebarn.com/shop/aquarium-supplies/coralline-algae-bottle/
Tank is almost 18 months old. Parameters were stable (although I was not measuring with Hanna until this month), through Mar/April of this year. Then things got out of hand (lack of housekeeping, overfeeding, blah blah blah).
Cycling wise I used Red Sea Mature kit. That being said, after the first month of cyling, I did use Vibram on a weekly basis to fight the "ugly". I know this was bad, etc. This was before the Vibram being an algacide news became more widespread. I never had Ditoms, and assuming that is maybe why I am seeing this now.
I don't know if the Chemiclean (doubful), or the rip clean/peroxide dip maybe messed up the good bacteria on the rocks. In scanning the forums, it doesn't look like that is the case, but I really don't know
I think its more likely I am just dealing with alot of algea death. As P increased, I added GFO and bottomed out the P, and then created a major N/P imbalance.
As a side note, I did just add in some of that Coralline Agea stuff (plus a small live/mature rock) in to see if I can encourage Coralline.
Very open to thoughts/feedback. Thanks!