For Sale CAUTION

I was going to suggest that as well. Since your getting the fish out of there just go ahead and pull the rock and treat it to remove phosphates, I'm sure they're your big problem now. I'd do all new sand as well.
It's a nightmare battling phosphates and nitrates on a running system. It seems you can go through pounds of GFO and every other media and nitrate reduction method and barely make a dent in things. It's been an ongoing battle for me although I never had hair algae, but I think that's because my fish keep it in check pretty good. There have been several times I have considered just tearing down and basically starting from scratch. I just don't want to get rid of my fish, and have no were to keep them while I cycle a new system.

 

Can you fit them in a small 10 or 20 gallon? Just something temporary you can set up while you restart the big tank?

 

A few things to consider:

Correct me if I'm wrong but "cooking with LC" isn't really a thing. LC precipitates phosphate out of the water column, so if you don't have any P in the water, LC is not going to do much of anything except "grab" and P coming out of the rockwork. I'm not sure how long LC remains active in the water column without some P to bond to? I think most people use GFO while cooking because it's not required that it be immediately used - it picks up the P as it gets drawn out in the cooking process, but with no light there is no algae to take up that P so LC isn't really "needed" per se. I may have that completely wrong so feel free to correct me!!

If you powerwash, that will get rid of loosely bound organics but not hard-bound phosphate. Phos bonds with calcium to form a crystalline matrix on the rock that needs pH below 7 to be chemically removed - hence the acid bath idea. But that kills the rock and you have to then cook/cure it, your tank will go through the 6-12 month maturing cycle, etc. I've also heard from people that it doesn't necessarily solve the problem....I consider this a bit of a last resort.

Personally I would try cooking it in a tub with a skimmer and a whole bunch of GFO, do the dunk thing 2x/week and let bacteria do the work, you will be left with cured rock. FWIW the part of the bacterial process that is theorized to happen during cooking as it relates to bound phos is called bacterial cleaving, where PSBs (phosphate solublizing bacteria) create momentary low pH zones that release the bound phosphate. The theory is that when you have zero phos in your water but you rocks are growing algae like nuts, this is the process that is occurring and algae is working symbiotically with the PSBs and taking in the phos and that's why you're getting it.

A lot of this is anecdotal because to my knowledge no one has studied and conclusively proved that PSBs exist in reef tanks, but it positively happens in the ocean. I come across this precise issue (no P but algae on rocks) in scrubber Q&A quite often - sometimes when someone adds a scrubber and their P drops way down after being elevated for a while, you get an algae explosion in the tank. That's (theoretically) because while previously phosphate has been depositing on the rock, now it's leeching. I don't know if this is what is happening in your tank but it sure sounds that way to me.

 

That's part of the cooking process. 2x a week, you set up 2 buckets of water and dunk in bucket 1 a few times, then dunk in bucket 2 a few times, then return to cooking bin. The gunk that comes off will surprise you.