Let's trace it back out biologically just to make sure using only submersion time descriptions
Was any rock or sand wet vs dry when you set up the tank
From what I can tell from the post, this aquarium has fish in it right? If so, they die in twelve hours or less within a system lacking bacteria to process ammonia. I'm reading this tank has had water a few weeks right
There is no possibility for a system to process only 98% of a given bioload and only leave a small portion unoxidized, it's either death in twelve hours or the tank is cycled. Your tank is full of surface area, it scrubs all avail ammonia quickly.
Also, it appears the rocks are not barren white dry base rock, are there any live components to the rock like coralline, fanworms, sponges or any pods? At one point in the pic it looks like a red mushroom coral is on the rocks, what living creatures are associated with these rocks if any
Regarding algae the tank is ok now for sure, looks great, but in two more months some green hair algae pops up and that's a fork in the road. A choice time
Many choose to leave it in place
Some, a few, choose to kill it off manually vs let it take over. Hand gardening until maturation takes over and we can work less, this is better than letting the tank self invade
I run algae fix work threads that run eight years per thread, nearly every entrant is trying to recover from permanent uglies that didn't go away. Be researching direct kill methods vs any method that has you dosing the water or measuring it to control algae. Kill algae directly. Brainstorm how you can remove rocks for external work as needed in order to be opposite of rescue thread entrants. Mostly no one agrees with me on this
Which is why I have multiple eight year work threads heh/keep em coming we love the challenge
For example, if gha popped up on your top rock easily lifted out you could:
-Do nothing, let it grow, we are told the uglies phase is expected. The masses always follow this option.
-you could break rank with loss technique, lift the rock out, and use a propane torch to burn the algae right off gone, set rock back. Cheat your way to no algae. Doesn't have to be fire, that's just an example of creativity and not willing to lose a tank at all. Ten other kill options exist. Could be a simple paste made of kalk to burn the patch, doesn't matter. The resolve matters not the tool, I use peroxide. Externally
The larger the tank the more cautious we have to be in preventing takeover. Only nano reefs get easy resets. We are moving away from cycling planning and into tank planning since all the biology is about to start running it's predictable path