Preventing Mustard Algae

[red-beard]

Is there an estimated HOCL to prevent Mustard Algae?

I've been adjusting my CYA to 30 and according to the water chemistry page, anything above 3.5 ppm FC (HOCL of 0.050) should prevent algae. I expect this is for green algae, because it does not stop Mustard algae.

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

www.troublefreepool.com

Anyone have any data on preventing Mustard? At 30 CYA, regular shock is 13 ppm FC (HOCL of 0.38). Mustard shock is 19 ppm FC (HOCL of 0.68). If I use the same ratio, HOCL of 0.050 goes to 0.090, or a FC of 5.5. Any thoughts? I'm thinking of keeping my FC no lower than 6, which means about 9 ppm in the morning.

Dammit Jim! I'm an engineer & chemist, not a microbiologist...

 

[mas985]

Normal FC targets should be able to keep mustard algae from starting. However, once you have it, it takes a lot more to get rid of it. You need to follow the mustard algae article in pool school to eliminate it. If it keeps coming back, you have not eliminated it.

Mustard Algae

Today We are going to show you how you can get rid of mustard algae in your pool. By following the steps in this guide and with no expensive chemicals.

www.troublefreepool.com

 

[Ansem]

I’m interested in this too.
I had my pool Chlorine levels at 7ppm since opening for the summer. Lowest it went was 5ppm. But for some reason I got mustard algae growing on the walls. Everything else is balanced So annoying.

 

[red-beard]

I found in the archives a post detailing a minimum HOCL of 0.07 ppm to prevent Mustard. This is 4.3 PPM at 30 ppm CYA. I am now targeting 7.5-8 ppm for my daily start value. Which means I'm adjusting my FCL to 7.5-8 ppm in the evening. I'm losing about 3 ppm per day FC. I will test this for a couple of weeks.

 

[red-beard]

I’m interested in this too.
I had my pool Chlorine levels at 7ppm since opening for the summer. Lowest it went was 5ppm. But for some reason I got mustard algae growing on the walls. Everything else is balanced So annoying.

I think there are a few parts to the problem. 1) The Mustard occurs where water doesn't circulate and is shaded - Solution, maybe adjust jets or increase pump speed. 2) There are bits of algae in crevices that are hard to eradicate. Need to pull lights and any water dead spots and circulate. Also run the boost pump to circulate that area. I run my hot tub for 30 minutes a day to full circulate that line. I'm keeping notes on what I try and what works. I've SLAMMED the pool a few times, including a week at 30PPM. Of course, the CYA was 120 at the time.

 

[red-beard]

So far, so good.

 

[red-beard]

6 weeks later update:

I raised my CYA to 30 and have kept it at 30, accepting the potential chlorine loss. This puts me into the 2-6ppm FC region. I originally was raising to 8PPM FC each night. For the past 3 or so weeks, I have only raised it to 6 PPM. I've even "missed" a couple nights and put the chlorine into the pool in the morning. I did add some CYA when we had 8 inches of rain, to get it back to 30 ppm.

I'm losing about 2.3-3 PPM FC a day due to sunlight, so the CYA level is fine. I lose almost nothing overnight.

Raising to 6 FC means I rarely drop below 3 PPM FC. And raising at night means at least 12 hours per day at 6PPM FC. I expect I have less than 6 hours per day below my 4.3 target. I don't think I'm giving the mustard a chance to grow!

A couple of other things, I replaced my lights, cleaned out the niches and then "sealed" the cord conduit with a split rubber cork. I also power washed (under water) all of my inlets and outlets.

The pool has NEVER been better. And I have the team here and all of the information on this site to thank.

Thanks!!!