Just did the ascorbic acid trick. Had a terrible stain this year when opening. Was told by the pool guy that it was algae and he sold me al kinds of stuff, that didnt work. Then told me the stain was coming through from the other side and I would probably need a new liner. Did some checking and landed here. Checked the stain with a vitamin C tablet and it instantly cleared.
So got the PH and Chlorine down and treated with ascorbic acid 2lbs in 15000 gallons. Most of the stain cleared but not all, figured it might take more than one treatment to get it all. After 90 minutes I put the Metal Free in and turned it to filter. Pool immediately clouded up and I thought I really screwed it up. But I could see that the rest of the stain was clearing off, I assume that is what clouded the water. Will check in the morning and hopefully all is well.
On another note, I did switch to the BBB method due to high CYA levels and repeated drain/refills to correct that. Seems that everything the pool place sells creates other problems, then they sell you something to fix that and yet another problem is created. The BBB method has been very easy once everything is in balance, 5 minutes a day to check and adjust and way cheaper than pool chemicals. Once this stain is cleared and water back in balance Im going to adjust the borate level for some real clear water.