It's been many years since I've needed to post...due solely to the sage advice of those in this forum. Thank you for giving me the knowledge that has kept my pool crystal clear (with only the use of liquid chlorine and muriatic acid) for so long.
Unfortunately, I now have an issue and could really use your advice. Apologies for the long post, but I wanted to ensure you had all of the details and didn’t want to pre-suppose what you’d find relevant.

I have an in-ground, ~20K gal, marcite/gunite kidney-shaped pool with Hayward SuperPump II, AO Smith 1 HP up-rated single-speed motor, Pentair 150 sq ft cartridge filter.

Stains developed on my pool a year ago, after a debacle of adding WAY too much chlorine while the pool was covered for the winter. I thought it was deterioration of the surface, lived with it for a while and was about to hire someone to resurface it, but then thought to check the forum first and, of course, found the right answers. I did a quick Vitamin C test and determined that I was dealing with metal stains, NOT surface deterioration, and proceeded with the ascorbic acid (AA) treatment process. I bought the recommended products (via the links provided in the instructions so that you guys would get the Amazon percentage): 3 lb bottle of AA, Kem-Tek 60% polyquat, Jacks Magic “The Pink Stuff”, skimmer socks, and a 1.5 ppm Culator.

K2006 Test Results prior to starting: Cl=2.5, pH=7.6-7.8, Ca=300,TA= 80, CYA=0 (!! not sure how THAT happened; 6 months ago, it was 50). I added muriatic acid, which brought the pH down to 7.2. I decided to start the process even though Cl was not at 0, figuring I’d just add more AA if necessary (and with CYA at 0, I assumed the Cl would go down quickly anyway. Here’s the subsequent chronology of what I did.

03 Nov: Removed the filter, started the pump, then added 8 oz AA. After an hour there was not much difference, so I added another 8 oz AA. Checked again a half hour later and it was definitely working. Checked again another half hour later and there was no further change, so I added another 8 oz AA.

I continued in this way (as some staining still remained) until all 3 lbs of AA had been used. Testing revealed Cl=0, pH=7.0 so I added 8 oz of algaecide.

04 Nov, morning: Some stains still present, so I purchased an additional 2 lbs of AA (from a local Vitamin Shoppe) and ended up using all of that as well.

05 Nov: That did it! The stains were completely gone from the surface. pH was <7.0, so I used a bit of Borax to bring it to 7.0, then went to add the HEDP. Here’s where it got tricky. The instructions say to add HEDP “at the rates shown below” but there are no rates shown. I bought only 1 quart-size bottle and realized (too late) that it was not near enough. I put the filter cartridge back in, put the Culator in the pump skimmer (under a sock), added the 1 qt of HEDP I had, added 8 oz more of algaecide, and put in an Amazon order for more HEDP.

06 Nov: The pool is starting to get cloudy…not bad but noticeable.
07 Nov: The cloudiness has remained…no worse though. Added 8 more oz of algaecide.
08 Nov: The pool is now so cloudy that I cannot see the drain in the deep end or even the bottom step in the shallow end.

09 Nov: The HEDP arrived! I added it (2 quarts), and 8 more oz of algaecide, then waited 24 hours to rebalance the water. I also put 2 lbs of stabilizer in a sock in the skimmer in preparation for reintroducing the Cl.
10 Nov, morning: I decided to continue the process regardless of the cloudiness, thinking that rebalancing the water might just take care of it. I added a 1/2 box of Borax to start bringing the pH up and another 2 lbs of stabilizer.

10 Nov afternoon:
• 12 pm: Cl=0, pH <7.0. Added another half-box of Borax and a half gal of 11% liquid Cl (added directly to the water in the deep end, as I still had a sock full of stabilizer in the skimmer).
• 1 pm: Tested Cl=0.5 ppm and pH test is turning purple! (huh??)
• 2 pm: added another half gal of Cl.
• 3:20 pm: Tested Cl=1.5 ppm
• 5:30 pm (stabilizer has fully dissolved (probably cuz the pump is running 24/7): Tested Cl=1 ppm, pH=7.0-7.2 (yep…test is now working ok); CYA = 35-40 …added 1 gal of Cl

11 Nov
• 7:45 am: Tested Cl=2 ppm; ph=7.2…added a half gal of Cl
• 2:30 pm: Tested Cl=2.5 ppm; pH=7.2…added a half gal of Cl

11/12 (this morning): Tested Cl=3 ppm; pH=7.2
The cloudiness has decreased slightly…I still can’t see the drain in the deep end, but I can now see the bottom step in the shallow end.

What do I do next??