fighting mustard algae

[Kateyru]

I'm starting a new thread as my old, long one seems to have gotten lost in the shuffle.
I'm pretty sure I have mustard algae, thanks to info from you guys. My most recent test results were on 6/5 as follows:
FC =17, CC = 0, pH = 7.6, TA = 90, salt = 3400. A problem is the CYA. I thought that CYA = 65 on 5/30 but tested again on 6/4 and got 50. Test results per K-2006. About the FC = 17, I was in the process of shocking so I could do mustard algae shock.
On 6/5, I added muriatic acid (per Pool Calculator specs) to lower pH to 7.2.
On 6/6 in the AM, overnight FC loss was < 1 ppm and CC = 0 so I started mustard algae shock treatment. FC that morning was 27.5 and I added 21 qts of bleach to add 14 ppm so I would be at 48.5 ppm (over mustard algae shock level) AND turned on SWG as I had to be gone all day. At 7 pm, I turned SWG off and tested FC = 31. I added bleach = 8 ppm.
On 6/7 early am test results were FC = 37. I added bleach = 12 ppm and turned SWG on again as I was gone most of the day again. At 12:30 pm, FC = 35.5 and I added bleach = 2 ppm. At 7:15 pm, FC = 29.5. I turned SWG off and added bleach = 16 ppm.
I have brushed walls, sides, ladder, etc, ever time I've added bleach.
I have not been able to keep FC at or above mustard algae shock level for 24 consecutive hours so far. Tomorrow (Fri, 6/8) I can be at home all day if needed. Please advise.
thanks.
Am I way off track on this?

[Kateyru]

Correction for last addition of bleach, it was 14 ppm. Estimate FC was then 43.5 This morning at 6:30, FC = 36.5. Big drop! Added bleach = +6 ppm so estimate FC = 42.5.

[chem geek]

The last I recall from the other thread is that you have a light in the pool but didn't remove it to get into the light niche. There may very well be a lot of yellow/mustard algae lurking there which means that even if you kill it off in the bulk pool, it will re-introduce itself as soon as the chlorine level drops down below around 15% of the CYA level. It's one of those choices you have to make -- either find and kill the last of the yellow/mustard algae in all dark places it hangs out in the pool or deal with having to inhibit it with one or more of 1) a higher than normal FC that is 15% of the CYA level or 2) use an algicide (such as Polyquat 60 weekly) or phosphate remover at extra cost.

[Kateyru]

Thanks, very helpful. I'm glad to have options tho there is a definite best (get the darn light out). One more question...if we can get the light out after FC is much lower and we can try to remove while we are in the pool, I'm guessing that I would have to do the mustard algae shock treatment all over again, correct?

Also, based on additional reading, I think the stuff I see around the bottom edges of the pool is probably stains rather than mustard algae.

Many thanks again!

[BigDave]

You probably can get in the pool (CYA 50+ppm FC 30+ppm). Wear an old suit(you don't care about), cover your hair, work quick, take a shower. maybe better than letting it drop, doing the work and then starting again. Your choice.

[Kateyru]

I didn't remember correctly about the light. My husband got in the pool before I started shocking. The screw was so rusted that he was afraid it would break off and cause more serious problems. any suggestions about that?
I'd also thought I get our pool guy to try to remove the light as he likely has more experience....tho a service call is $75.
Thanks!