well they w only be out a few mins, that hiding wont matter. my offer was to lift out the rocks and treat externally as you are doing, rinse really well, dip back in a bucket of clean sw as an extra measure if you can for the extra mile rinse, and then reposition back in the tank.
Always keep in mind the predicted sensitive animals, your fire shrimp, against this method as any mistakes w kill that shrimp. Its also easy to never expose that shrimp to peroxide, but not rinsing correctly etc can do it, and IMO you are saving an ecosystem at the cost of an inhabitant=worth it but not everyone agrees. they only rate peroxide effective if 100% of nontargets are safe and your target never shows up again after a single dose lol (hey thanks for the one off standard nothing else in reefing is expected to provide ha ha)
peroxide is dang good here, but needs a few cycles to beat back this animal that grew in cycles from a small mass to a dominant one.
but the prediction is you will have minor growback, this wasn't acting on the first minor mass but we will still win. you will need to retreat spots again, but we shall soon see you are treating with something powerfully effective against that algae and very predictable in its timeframes and action.
the next few times you are removing rocks to zap, thats the price for waiting but we are in the process of saving this tank and its my friendly offer nobody could have starved this out with nutrient controls. it was get a grazer lucky and dont cheat, or cheat this whole tank into compliance and im a purveyor of option b.
so they are without their rocks only a few brief minutes
also, consider any detritus kicked up here, that remarks on how your tank is storing wastes and indeed feeding the algae in addition to what it can naturally harvest anyway in super clean waters. these clouds of dust if any are a real ammonia risk, making something look like a peroxide death when in fact it was a mini cycle by not having the nutrient stores in check. those are confounding details to consider in tank workovers.
it helps to isolate or quarantine sensitive animals in alt tanks as we kick up filth and dose this or that. if not possible, we work around keeping everything inside by doing small sections slowly, so these waste release events are sized correctly.
this needs to be a period of a week or two during these remove and treat actions that you are removing waste and changing water more than normal, some of the physical work not done now needs to be to lessen any nutrient sinking as a true long term balance issue.
lastly, there are plenty of natural examples where this kind of algae and many others takes over reefs when nutrient levels aren't to blame, merely lack of grazing, and as of now we are chemical grazers.
