I put a vit C tablet on this rusty looking stain. After the tablet dissolved, it left a charcoal colored stain. Perhaps I left it on too long.

Taylor test kit DPD
Hayward DE filter
This is a 20,000 gallon plaster pool
Inground (broken) cleaning system
CYA well over 300
PH 7.4
FC over 15- I diluted with distilled water to get my cya and chlorine readings
TC- less than 15.. It's hard to tell when the readings are so high but it was ligher.
Calcium- I quit counting after 100 drops.
TA 200

Right now we aren't running the filter because there's a plug stuck in the skimmer. (on another thread)
My friend just moved into the house and the pool was a mess. The heater is in really bad shape and disconnected...but who knows how long the water was running to/thru it while it was rotting away.

We'll drain this weekend and start over.

If I understand this correctly- Drain and refill to get CYA 30-50, Drop the chlorine to 1ppm, PH to 7.2, add absorbic acid (gotta look up the amount). Add 2 bottles of sequestrant- run the filter for 24-48 hours and then slowly raise the chlorine level.

Did I miss anything?