That's why!!!
Too many fish too soon and too much light.
Can't do anything about the fish, just don't add more for a good while!
But you can shut off the lights altogether if you want. Certainly run them at a minimal level.
No more than 10,000 #lux.
Once the tank cycles a bit more, coraline algae will have taken over more real estate.
If you don't plan to have corals, I'd plan to carbon dose the tank (e.g. vinegar)...but not for a while.
See if things just settle down after the cleanup crew has had time to munch and coraline algae has had time to march forward. If you do decide to start carbon dosing, start with a very small dose, and don't start unprepared....research!
Adding stony corals would help
a lot if you were planning to do that. Don't start unprepared though....research! (They take a while to kick in their effects, too.)