sooo
not a tiny tank ha, well done.
plus, that cotton candy type shown is MUCH preferable to asparagopsis and this isn't a terrible strain. This is my initial musings on your pics based on ten thousand peroxide challenges and about 20 involving exactly that strain:
-not a nutrient issue, so don't modulate nutrients those SPS are used to in response. That is a specialized hitchhiker and not particularly common on reef substrates...it is a requisite hitchhiker and all that means is once its dna is eradicated by whatever means, it can't come back until re import. No matter how much N and P someone added to my reef, that type of algae doesn't exist in mine and can't be elicited, but what does exist are the ubiquitous invaders like GHA strains and cyano strains...everyone gets those in response to nutrients ups and downs so those are the ones I like to tune nutrients to battle.
yours is a matter of targeting, tank continues in stasis
fluc has a 30% chance of working but I say its valid to try, since fluc didn't show in the giant fluconazole threads very much collateral loss, as a pattern, at all. its a fairly safe hail mary pass to try.
regarding peroxide testing and work you should test model a couple of simple things to learn about the invader, it doesn't mean you have to take your huge massive tank apart like us spoiled nano'ers do, or even use peroxide any further than basic testing.
part of the way we arrest tank invasions in 2018 in our large threads is by discovering what it takes to cause recession on a small, demonstrable scale.
the old way was do X to your tank, cross fingers, hope nothing dies and nothing grows back and that the target dies. By using 2 test rocks, and not your whole tank, we literally undo that entire old order of operations and address every matter in reverse:
by pulling out only two top rocks, one for harsh testing and one for light testing, we darn sure are about to get a guaranteed kill, we don't do anything to the nontargets, and we're about to learn about growback without sacrificing anything in our tank.
so, we have you pull out two accessible target rocks. on one of them, set the target rock with no corals only target briefly into a bucket of saltwater where fresh 3% peroxide was set at dilution of 2 ml's per 10 gallons of water...so in a typical five gallon bucket input one mil peroxide and set the test rock in it overnite.
next morning, lift the rock out, lightly rinse over in fresh salt water and reinstall, look to see if the cotton algae dies after being exposed to the max dilution your whole tank can take based on nontargets pictured, if you ever get desperate. *****red algae are slow dying, 7 days until they turn hot pink which is the death coloration phase in rhodophyta treated with peroxide** on day 3 you'll think nothing worked. give em 7-9 days eval
on test rock #2, they get the dentists rasp w bleeding technique.
Take a large steak knife, and absolutely meanly rasp that algae off the rock. scrape, gouge, be mean, the rock has scars but that algae was debrided by metal force and you took out the substrate it was anchored to.
when that rock is scored clean of algae by hand and rinse, then put straight 3% peroxide back across the former growth areas you just cleaned. undiluted, as a cellular rinse.
we just mimicked the method of taking out every rock you have and doing the single most affective thing possible while maintaining its bio filtration, peroxide doesn't harm biofilters in marine tanks at all, in any way.
on test rock #2, we watch for growback over 9 days while watching for test rock #1 to succumb, hopefully, but maybe not as that's just the ideal. you might get lucky with a susceptible strain where when/if you get desperate, a calc'd dose of peroxide shot into the reef simply kills it.
use and ponder other methods first, but always know something about your invader as a worst case scenario.
you can biomodel anything from fluc to other means in a 5 g bucket before exposing that bad boy to guesswork.
I know that's a a lot of type but yours takes planning this is not easy. ill hunt down a quick example of a similar kill we did real quick to show, only this tank was way smaller ha you've got a challenge.
**if you are contemplating vibrant, then dose it to test rock #3 in a circulated and heated bucket and don't take risks with your whole tank. Biomodeling is the new rule of controlling invasions in large tanks for sure. its not method specific, its modeling specific. I know of zero known cures for that target using Vibrant though its relatively safe to try as a model in my opinion. Vibrant is for a very tight genus of targets