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!

[Kateyru]

Update: Pool guy wasn't willing to try to remove pool light. Hope no lurking algae back there but time will tell. I removed the treads on ladder the other day while still shocking.

I'm now letting FC drift down. Water looks great, very clear. FC = 7.5 this morning. On Thursday, CYA wasn't showing up when tested (not sure what happened) so I added 3 lbs. through a sock. That being 1/2 the amount needed to get CYA to 70. I am leaving town in the morning for 2 weeks. So, I won't get an accurate read on CYA until next Thursday???? What do you suggest about adding more CYA? I'm checking FC and pH daily.
Thanks.

[aylad]

If you're planning to run your SWCG, you need to add whatever amount of CYA the manual for your unit calls for, and that' usually around 80 ppm. If you are not running your SWCG, do you have somebody to take care of the pool while you're gone for 2 weeks, so you don't have to start over when you get back?

[Kateyru]

Yes, I'll run SWG on regular schedule. My manual says CYA should be 60 to 80. So I should go ahead and add enough CYA NOW to get to 80 ppm? My husband will be at home but he is not overly helpful with the pool. If I go ahead and add CYA, the FC and pH should be tested everyday for several days? Hope I can convince him (the husband) to test...
Thanks.

[aylad]

Yes, go ahead and add whatever amount you need for your SWCG. The FC will definitely need to be tested (and adjusted if necessary) on a daily basis. The pH should be okay if he tests it every few days....