How long to hold at 15ppm with mustard algae

[SoCalBoo]

Posted question re: ch, ph and TA w/ mustard algae on pool balance/chemical subforum the other day. Very good and sage advice from others. Thanks.

I have been holding ch at/above 15ppm for 2 days. No sign of mustard algae since last night (I have been brushing twice a day...yesterday morning, some algae had reappeared overnight since brushing the preceding evening, but nothing since then).

So how long should I hold?

By the way, if it matters:

22,500 IG gunite/plaster pool w/ 7 ft spa. Single spillover, no waterfalls. Autopilot SWG. Solar.

This afternoon:

TC - a little above 15ch (don't have real accurate kit)
CC - none registering
ph - 7.4, but slowly creeping up (7.2 yesterday)
TA - 110
don't know salt or CYA
Autopilot trisensor unplugged (so cell won't generate while superchlorinating)

[mwsmith2]

Well, personally, I'd hit it with the starting dose of polyquat if you've got mustard. The high Cl seems to slow it, but doesn't seem to be able to take it out. Polyquat does the trick for me.

YMMV

Michael

[CarlD]

While you COULD use a good dose of PolyQuat, I have to disagree with Michael on one thing:

Without knowing your CYA we cannot know if an FC of 15 should be effective or not.

If you have a CYA of 100, you need to keep FC at 25ppm. 15 won't be successful. However, if your CYA is 30, then FC=15 should be effective.

Also, a caveat: When you dose your pool with PolyQuat, your FC will fall DRAMATICALLY. You will need to get it back up. I don't know the chemistry, but PolyQuat does depress FC, and lots of PolyQuat can really push it down.