fighting mustard algae

[chem geek]

Yes I would lower the pH now. From what we have more recently learned, the pH test is actually not inaccurate at first even at higher FC levels when there is CYA in the water. At high FC what you will find with the pH test is that it initially gives the correct reading and then over about a minute or so it turns the purple color caused by the high FC oxidizing the indicator dye. Apparently, the lower active chlorine level from the presence of CYA slows down the rate of the FC interference in the pH test. So your pH reading of 8 is likely correct and you should lower the pH quite a bit (at least to 7.2 if not 7.0) before shocking.

As for the yellow/mustard algae shock level, you don't have to be exact about this. 35-40 ppm FC is fine. It isn't like there's a magic number where it works -- higher just goes faster.

[Kateyru]

pH = 8 was before I started shocking...which I'm doing now. I'll add acid to lower pH now.
I'm such a "rule-follower" that I try very hard to do exactly the right number...glad to know it's not that exact. How long do I maintain mustard algae shock level?
Final, for now, question...previously you said that I could either keep FC at 15% of CYA, use polyquat 60 weekly or use phosphorus cleaner weekly re: mustard algae (and possibility/likelihood of not getting rid of all of it since I couldn't remove my light and clean the niche). Will any of those options actually get rid of the mustard algae or just keep it out of sight?
Thanks so much!!!

a few minutes later...
Hmmmmm...I just tested FC. This am at 7, FC = 41.5. I had to be away most of the day so turned SWG on at 50%. Just tested at 4:15 pm, and FC = 23.5. Quite a drop, considering SWG was running. So, do I start all over re: shocking? Just added acid to lower pH. How long before I add bleach?

[chem geek]

The chlorine will drop during the day. What's more important is how much it is dropping at night. Just add more chlorine to raise the FC again. Shocking is a process, not a one-time dose. You'll maintain the shock level until all the visible yellow/mustard algae is gone and your overnight chlorine loss is normal (usually < 1 ppm FC but at the higher shock level it might be OK to be a little higher than that) and then to be sure you'll keep it at shock level for another day or two.

As for those other methods of maintenance with higher FC or polyquat, etc., those may not be necessary. Let's see if we can completely get rid of this so you won't have to use other maintenance methods. Those methods just keep any yellow/mustard algae in check and they don't completely get rid of it.

[Kateyru]

Ok, I think I've got the plan. Shock at higher levels till no visible algae and overnight chlorine loss is normal...just like regular shock process.
I wasn't sure it was possible to get rid of all the mustard algae since I can't get pool light out.
I think this will take awhile and lots of bleach. I added 4 jugs of bleach (182 oz. jugs) last night to get FC = 40. This morning at 8:30, FC = 33.
Off to Dollar General (best price on bleach there and at Costco, btw) to get lots of bleach...should have bought stock
Important question, would you swim in this, FC = 40? It is hot as hades in Alabama!!
Thanks so much!!!!!!!

[Kateyru]

At 12:30 pm, FC = 37 so I added 2 more jugs (182oz. each) of bleach then measured pH. I added 50 oz. of acid last night based on pH of 8 BEFORE I started mustard algae shock. The pH is currently over 8. Do I add more acid?
Thanks.

[PoolDoc]

You need to keep your chlorine high -- I haven't re-read the thread, so I don't know how high -- but you ALSO need to keep your pH in range. Add some acid, until it's below 7.8!

[Kateyru]

Okay. What about TA which was 48 on 7/31?
Thanks.