48 hours into a SLAM. Initially took pH to 7.4 with acid and mustard algae shock level according to pool calc. Then let FC drop to SLAM level and have maintained 16 FC based upon 40 CYA for 48 hours. Overnight test showed pool at 15 FC, 0 CC, and water is pretty darn clear. ( no direct sunlight as of this writing so will know for certain about clarity in an hour or so..) Sounds pretty good right? Should be done right? However after daily brushing and vacuuming I still have what looks like algae/mustard yellow stain on shady side of deep end. No amount of brushing is knocking this stuff off. Tried wire brush as well and no go. What do you think? Keep at FC 16 for another 24 hours, keep brushing and see what happens? I have never had this kind of staining except when I screwed up and got an algae bloom so I can't imagine what else could possibly stick to the side of my deep end this way. Thoughts?