Update
Alright after a super fun 7 hours of scrubbing, some knife-on-rock scraping, 3% peroxide spray and scrubbing and rinsing....this is where we are. (See pictures).
I'd say I got at least 90% of the GHA out of the tank. (For now).
Heres what I learned: (just for me personally) scraping live rock with a knife is 100x more difficult than youd think and its insanely time consuming. I did part of 1 rock. Sorry. Dental precision is not happening here. :/
Also, a day and a frozen food feeding later, those low phos and nitrate levels are still barely there, so I dont think gha was locking up any nutrients and making them untestable. I can retest in a week if anyone wants to see if that changes w longer than a day.
So. Now 90% GHA gone, some corals broken, some angry as he**, 1 missing, 1possibly dying, and 4 displaced and need remounted.
To try to limit gha regrowth:
1. Huge cuc- let's see if they can keep it in check
2. Adding Seachem Stability to the tank (bacteria blend) to boost bacteria since a lot of peroxide was used and to try to help mitigate gha return. (No one sells vibrant around here and wanted to start w something).
3. GFO reactor going back on for a while (sorry softies) to see if what little seems to be in there can get removed.
Question: do I need to feed the bacteria w carbon dosing (ex vodka) or will it be fine?