fighting mustard algae

[aylad]

I wouldn't drop the pH just yet, let it get closer to 8.0. When you do lower it, bring it down to 7.5/7.6. This will drop your TA. When the SWCG brings it back near 8.0, lower it again. You will be performing the TA reducing procedure but slowly.

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[Kateyru]

Hi Team,
I'm back again...after being gone for 3 weeks. A 2-week vacation, 1 week at home and another 3-week vacation is great for me but not so good for the pool.

test results on 7/4 were as follows:

FC = 10.5
pH = 7.7
CYA = 50
TA = 90
I added stabilizer before I left town trying to get level to 70. I asked husband to check FC and pH daily and to let me know if FC got to 5 and when pH got to 7.8 so he could add acid to lower and get TA down. He says that he checked every few days and FC never got down to 5 and pH never got up to 7.8. He only added salt while I was gone. We had lots of rain and high temps of 100 for many days.

Test results yesterday:
FC = 8
pH = 8
TA = 48
CYA = 60 to 70
and, natch, I have algae again.

I am now shocking again (at 20 since CYA is 60-70).

What made TA go down like that...rain, debris in pool????

FC stayed high (somewhere between 7 and 8) so what made algae return? pH too high?

After I shock, what is next step? Raise TA? Raise CYA?

Thanks.

[BigDave]

Mustard algae? I don't think you ever killed it all. You'll need to take the FC way higher than 20 and keep it there for a long time and brush everywhere it might hide. Please don't raise your CYA at this point.

[Kateyru]

I really thought I'd gotten it...the last test results before I left town were taken on 7/10 rather than the 7/4 results I posted in yesterday's post. On 7/10 results were:
FC = 5
pH = 7.8
CYA = 60-70
TA = 90
and the water looked great. Previously, the algae would show up when FC got down to 8.
Sigh...I'll do the mustard algae shock routine...regular shock till FC loss is less than 1ppm overnight then move to mustard algae shock levels.
Thanks.

[BigDave]

As I recall, you weren't able to open the light niche. It could be lurking in there. I believe ChemGeek advised that you'll need to keep FC above 15% of CYA to keep the yellow algae at bay if you can't get rid of it all.

[Watermom]

No need to do 'regular' shocking and then move to 'mustard algae' shock levels. Just start with the higher shock levels.

[Kateyru]

Will do! I just reviewed "mustard algae" section on TFP website. Rec is to lower pH before shocking. Do I need to do that or just shock at higher level for mustard algae? I need to maintain mustard algae shock level for 24 hours, correct?
Thanks.