The front right coral would sell for $300 alone in my city. You need to be spot feeding it with rods feed or something refrigerated, twice weekly, with small water changes each time. You bought a system that needs feeding and active hand guiding and water changes so that it never goes downhill and the corals are fed relative to their mass. Be busy with feed in/ water change out at minimum weekly, twice is better, and it will run.
Don't kill algae by altering water parameters
Kill algae off rocks by lifting up rock and killing the algae externally, outside the tank, brief air contact won't hurt rocks or corals. Set rocks back in
These are the right steps to start for that tank
Be active, instead of letting it sit there day after day untended. Every feed + water change buys more days of life for large mass corals
Left in place, low action, they look great for months but are slowly losing internal stores; not adding mass. The other corals will live well off the runoff feed from making sure the open brain is fed.
The right way constantly adds small mass by active feeding and water changes, averting any back sliding etc
Changing a few gallons each week a couple hours after a feeding is easy, is training for required dedication etc and balances export required for feeding such a coral