Mustard Algae with Crystal Clear Pool?

[apoteker]

Is it possible to get mustard algae and have your pool look crystal clear and pool chemistry stable? I have a 31,500 gallon pool and my chemistry readings are consistently as follows:

pH 7.6
FC 4.5
CC 0
TA 80
CYA 55
CH 60

Every night I test and add 12% liquid chlorine to get my FC up to 6 which I have as my target FC. My problem is that I have noticed that I have mustard algae forming in the pool which is very confusing to me. It looks like I will have to SLAM my pool this weekend to get rid of it but I don't understand how I even got it in the first place since I have been faithful in testing and adjusting. Any help would be appreciated.

 

[JasonLion]

Welcome to TPF!

It is possible to have mustard algae even when the water is fairly clear and FC levels are normal. However, it is also quite easy to mix up pollen accumulating on the bottom with mustard algae. Is any of the "algae" appearing on the walls of the pool on the shady side? Or does it only appear on the bottom of the pool? Real algae almost always grows on the walls on the shady side, pollen only accumulates on the bottom.

There is a good article in the Solving Problems section of Pool School with much more detail on Mustard Algae.

 

[apoteker]

Yes, unfortunately it is starting to appear on the wall as well

 

[Verndoggy]

apoteker - I have encountered the exact same problem here in Southwestern Michigan. My pool numbers are good, and consistently so, being maintained right at my targets:

pH 7.6
FC 5
TA 90
CYA 35

Still, the yellowish algae (started early this week on the shady south wall of my vinyl pool) is flourishing (was on all surfaces as of last evening - looked very much like pollen, but I'm pretty sure it's algae). Water otherwise looks good. Time to read that Mustard Algae article in the Pool School, I guess. Good luck with yours.

 

[apoteker]

Sounds like it's not that uncommon to have a situation like mine (or ours Verndoggy). I guess the next question would be whether to use a polyquat algaecide after I get rid of the mustard algae. Any thoughts?

 

[apoteker]

So the mustard algae article in pool school says to SLAM normally and then bump up to mustard algae levels for 24 hours. So I would shock at normal levels (about 20 something ppm FC level) and then bump up to mustard algae levels (about 30 something ppm FC levels for 24 hours? Would just performing a SLAM at mustard algae levels be sufficient?

 

[Butterfly]

So the mustard algae article in pool school says to SLAM normally and then bump up to mustard algae levels for 24 hours. So I would shock at normal levels (about 20 something ppm FC level) and then bump up to mustard algae levels (about 30 something ppm FC levels for 24 hours? Would just performing a SLAM at mustard algae levels be sufficient?

Complete the normal SLAM process first. You will be done when you pass the three required criteria. See red lines in my sig.

THEN, do the MA shock process. Follow that process to a T.

 

[Verndoggy]

Complete the normal SLAM process first. You will be done when you pass the three required criteria. See red lines in my sig.

THEN, do the MA shock process. Follow that process to a T.

Just completed the normal SLAM process and the mustard algae (or is it pollen, I really don't know) is still evident when I brush the bottom today (yellow/green clouds), but not on sides of pool. I passed all three of the criteria in your signature, Butterfly. You are saying to STILL move ahead to the MA shock process, right?