Slime behind Niche Light

18.5 x 38.5 Grecian 3ft shallow, 8.5ft deep. My assumption has always been 20-22k.
I did manage to get the water tested by a local store. This guy seems to be a straight shooter and I have no reason to distrust him.

After the bleach, I brought a sample to him this morning. The results follow.
CYA = 96 (Close to what I read from K2005)
ph = 8.1 (This blew me away considering it was below 7 before bleach additions)
fc = 10 (Said this is as high as he can test)
tc = 10
ta = 109
adj ta = 80
appearance = mod to severe cloudy (my assessment)
temp = 78
salt = not tested as I have not added any as of yet

Will retest ph this evening and post.
Hope this helps. Thx

Your volume estimate seems reasonable. Your pH and alkalinity levels are fine for now.

So . . . go ahead and add 2 gallons of chlorine each evening. Test using the DPD tabs @ 1:4 dilution (multiply x5) every other day. Skip dosing at 20 ppm FC; resume @ 15 ppm.

Brush the pool completely.

Report FC & CC results once you get the K-1515

Don't forget that to do the Taylor CYA test you should stand outside with your back to the sun and hold the tube in front of you looking straight down into it. You want strong indirect light for the test -- not direct sunlight and not weak indoor lighting.

Several days now and the water has seemed to straighten itself out. It actually has a hint of bleach smell which is far removed from where it was and the cloudiness has dissipated.

This morning...
FC=7-8ppm on a half/half diluted test. It appears to be dropping, albeit, slowly. Using the instructions (multiply by 2), I think this puts me at about 14-16ppm
CC=7-8ppm (appears non existent)
PH=7.2, 7.3
TA=100
CYA still about 100. I still don't know how it got this high. My readings must have been incorrect at close last year.
Clarity on a 1(bad) - 10(perfect) is about 7-8

Going forward I plan to give more attention to the niche light and those hard to reach areas that have proven to be problematic.

Thank you for everyone who contributed their knowledge and insight to this problem. IMO, this forum is the single best resource out there.

I'm curious how it's going, now.

Ben

It's going well. I have all but completely converted over to BBB with SWG. So far so good.

The water seems cleaner and more polished than ever. I know my CYA is still high so I am keeping my chlorine a little higher than I normally would at about 7-8ppm.

I found that my ladder was also harboring some of the black mold/bacteria (or whatever it was) due to poor circulation. I have since drilled a couple small holes at the top and bottom of each rail with the thought that this may help circulate the water to the interior as people climb out of the pool.

Going forward, I will be more proactive with my light and remove it from time to time for cleaning. I've actually toyed with the idea of injecting straight bleach in the small circulation holes periodically to try and stay a step ahead this time.

Thanks for all the advice, that was the nastiest water/crud that I have ever encountered.

I suspect that, if you can succeed in fully eradicating it, you won't experience problems going forward, due to your more consistent and educated approach to chlorination.