That's not a tough fix biologically actually, so glad to see that thanks for posting. The bare bottom is why, excellent. No filthy sandbed, rare for us.
I like to make predictions after seeing before pics
We can discern causatives from tank pics, not nutrient readings as a neat point. The cause of this invasion is very clear, so the inverse becomes the blueprint for the fix.
With pics we can check to see if the tank can pass a clouding test, this one cannot, to attain that state is core to curing this system. Dosing peroxide to water cannot fix a clouding test, so water dosing is 1/5th of the actual work needed for this tank.
A clouding test for reef tanks is twofold:
1. Is the tank under any imbalance or invasion
If so,
2. Can someone reach in the aquarium, grab rocks or sand, shake them hard underwater, and develop a cloud? That condition is keeper caused and not biological as a cause, and its keeper undone just the same (do a tank cleaning)
Pics show us bioloading, which isn't bad at all here.
They tell us if we have rooted anchored invaders, or blanketing ones, that type of ID is what matters above actual genus and species...
The fact the lysmata cleaner isn't dead is a statistical outlier, breed that one
they're top sensitive animals to dosed peroxide. Some have survived indeed
This tank simply needs to be taken apart and cleaned manually. Put back together with not one cloud ability in place, all invaders pre rinsed outside the tank and zero invaders in the tank, all at once, due to a total external clean and complete water change. Peroxide isn't dosed to the water, that's a hands off mode which causes invasions bc dead mass rots internally and recycles life forms that dead mass selects for...eutrophic organisms, degredation organisms, oxygen sappers, the indicated method here is a full tank instant cleaning with skip cycle reassembly. If this tank isn't huge, that's how to actually fix it.
If it's too big to take apart, peroxide dosing should only be used when the tank was made clean and the invader was pre removed however that needs to be done.
It's fully ok to just dose peroxide non specific and chart what occurs, but that's polar opposite of what will fix the tank. Our thread at least uses one test rock per tank where absolute fix wasn't modeled and proven, can you run a test rock real quick, easy model, just so we keep that theme going
We are always able to learn something specific about a tank invader, before action, which will concentrate actions on the target and reduce actions on non targets. The correct order of operations in eutrophic aquarium restoration is some element of keeper multiplied physical work ten times above normal running conditions, it's never something we add to the water although if that's the desired method for this tank we can still make incremental headway. Very glad you posted this challenge
