+ CYA = 50 ppm. OK
+ Still greenish and murky. OK
+ pH above 7.2. OK
+ Chlorine variable, but up to 8 ppm
+ Pool gallons = ~12,000. OK


Do this:

#1 - Continue with the pump on 24/7 and the DE topcoat.
#2 - Get a gallon of muriatic acid (Home Depot, hardware store, etc.) and add 1/4 gallon to the pool. (Glasses, gloves, watch the fumes: after opening, submerge the jug part way into the pool water, so you can pour with the lip only a few inches above the water. Add about 1/4 of the jug.)
#3 - Test the pH an hour later. If it's 7.2 or above, repeat.
#4 - Adjust a return eyeball so it's 'ruffling' the water surface.
#5 - That evening, add 2 gallons of plain 6% household bleach, poured slowly into the skimmer. (Pump ON, any tabs or other chemicals REMOVED!!)

Continue doing all the above:
+ Lower the pH each time it goes above 7.2
+ Repeat evening chlorine dose each time the chlorine is below 8 ppm FC
+ Do not add other chemicals
+ Backwash as needed, and re-coat with DE.

If, after 2 days, the green is not all gray (no green), then:
+ Continue with the pH adjustment
+ Change to 3 gallon bleach doses and a target chlorine level of 12 ppm

After no more than 3 days, report FC, CC, pH (measure midday when chlorine is lowest), TA, CH, & CYA.

Explanation (abbreviated):
Trying to lower your TA via low pH and aeration, to remove any calcium scale; trying to keep your pH low to facilitate this AND to avoid copper staining; maintaining high enough chlorine to control algae and gradually kill it, without copper stains (hopefully); gradually increasing chlorine as (again, hopefully) the copper comes out on the filter.