Opened my pool last Friday April 24 and knew it was going to be bad so no surprise really. However, never had algae this bad nor climbing the walls all the way to water line. Since I couldn't see the bottom of deep end, I didn't know what was down there. Scooped out LOTS of debris: leaves, pine straw, worms, dead salamander, and gunk. Scooping and brushing was an ongoing process, at least 5/day. Even in the rain. Filter required backwashing at least 2x/day. Ran it 24/7.
Initially, I just maintained chlorine. I did add quart of polyquat 60 on day 2. I went through 8 gal of 12% liquid shock total in 4 days!. Which was curious that it took that much and wouldn't hold at all. However, after pool began to clear I took a CYA reading - ZERO!!! And I closed to 40-50 CYA. So again, I lost CYA over winter dumping and algae bloom. I've always lost CYA but never all of it.
By day 4 I had hope. Clearing nicely. Decided at this point to get some granular dichlor at Leslie's to kill 2 birds with one stone: chlorine and CYA. Since I could pretty much see the bottom I threw in my aquabot. 2 hours later the filter bag required cleaning. Kept running it, and cleaned filter bag every 2 hrs. Tedious but effective. Worked on balancing chems at this point. Everything was good except ALK - 40, added 16 lbs of baking soda over 2 days. ALK now 100.
Day 8 (Friday 5/2) was a glorious day! Woke up to a nearly crystal clear pool. Some "dusty spots" in a few areas and will require shock level until CC are zero. My metals fell out of suspension and will need 1/2 - 1 LB of ascorbic acid but that is not high on my list. That can wait.
Never in my wildest dreams did I think this swamp could get cleaned in 8 days. But, it can be done. This is proof. Confession: As a newbie, there is no way I could have accomplished this. Thanks to this forum I have learned EVERYTHING about maintaining my pool. Thanks to all the mods!!!