Yellow/mustard algae, forever?

goofiness

Bronze Supporter
LifeTime Supporter
Jul 3, 2011
75
Stockton, CA
I've had intermittent yellow streaks/smudges along the North facing wall of our pool for years. I tried to convince myself that it was discoloration of the plaster, and would scrub with brushes, stainless steel brushes and a pumice stone. I would keep the FC around 4 minimum, 6 after adding bleach each evening. This year I finally faced the truth: Yellow/mustard algae!

When it showed up in May, I SLAMed to yellow/mustard levels (around 24) for several days. Passed the OCLT, clear water, streaks on the wall gone. Since then I have maintained FC at min 6, target 8. No more algae.
Recent tests: FC: 8, CC: 0; CYA: 35-40; TA: 80.

My costs for bleach and acid are double what they have been in the prior 25 years, keeping the FC level at yellow/mustard recommended levels.

My question: do I need to manage the pool as if I have Yellow/mustard algae FOREVER?

Thanks
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
14,575
Evans, Georgia
No, you don't. Depending on your sun exposure, you might want to tap up your CYA by 10ppm to help shield your chlorine a bit. Just remember to follow the FC/CYA guide chart--> FC/CYA Chart

Its been brutally hot lately in the south, not sure your way or not, but the chlorine usage tends to be highest towards summer like now.
 

Fuldo

Silver Supporter
Nov 23, 2017
227
Port Orange, FL
Your recent FC range is barely above that suggested on the TFP guide chart. Every pool is different and you've proven what works in your case, if I were you I'd continue your present practices. The small difference in your FC targets between previous years and this year aren't double, they're more like 50% more. Not sure why you should be using twice the amount off chlorine and acid, how much of each are you actually using? You may be trying to maintain your PH too low, many folks here including me wait for PH to reach about 8.0 and only adjust it down to about 7.7. That seems to minimize acid use and still keep PH reasonable. Just check your CSI occasionally to ensure you're fairly neutral (close to zero).
 

red-beard

Gold Supporter
May 27, 2019
553
Houston, TX
Having had serious Mustard algae issues for years, I replaced my water and brought the CYA up to 30 ppm. I am keeping it at at 30 because if I have to SLAM, it is far easier at 30 than higher.

That said, I started this season by raising the FC to 8 ppm every night. Night is important, since it lets to pool have high FC for a long period.

Second, I am running my pump 24/7. I want some circulation all the time to make sure water goes everywhere. I also run my spa for 30 minutes a day (no heat) to circulate the line.

I cleaned EVERYTHING. I replaced my pool lights so it was a good time to check the niche. It was full of trash from the construction 13 years ago! I also installed split rubber stoppers on the light cords to prevent water from going back and forth from the conduit. I took my power washer (gasoline) into the pool and underwater washed everything. I took apart the door weirs on the skimmers and cleaned. And power washed the skimmers. Oh and I was brushing twice a week!

Knock on Wood, I have not had a Mustard outbreak the season. After about 3 weeks, I reduced my nightly target FC from 8 to 6. But again, I am doing my additions each night. I suggest you follow what I did and hopefully you will keep the Dang mustard algae at bay.

As far as chlorine loss per day, it is usually around 2-3 ppm. I am at 30 degrees latitude (very strong sun) and my pool has no shade. This is "acceptable" daily loss. A higher CYA "might" reduce the chlorine loss a bit. But I know what is actually working on my pool.
 

goofiness

Bronze Supporter
LifeTime Supporter
Jul 3, 2011
75
Stockton, CA
Thanks to all.
We are in central California. Near 100 F, full sun around 9AM-4PM. I've thought about raising the CYA, but that would mean higher FC to kill algae, and probably more $.
I misstated prior FC levels. Used to keep it between 5/3, adding around 42 oz of 10% bleach each evening. Now, I keep FC 8/6, adding 56 oz bleach. so, it's not twice the cost; just seems like it.
I keep pH 7.5-7.8, usually adding 16-24 oz of 31% muriatic twice a week.
I have not done a real "deep cleaning", but do look at hose connections, water return inlets, skimmers for traces of algae.
So, bottom line, I need to keep FC at yellow/mustard levels from now on, even with a "clean pool" at present. I suppose it's easier than having to SLAM when it may be inconvenient.
 

red-beard

Gold Supporter
May 27, 2019
553
Houston, TX
Don't worry about the pH too much. I let mine float to 7.9 and then drop it to 7.7. It drifts back up over 3-4 days. I have a near constant breeze that probably causes CO2 outgassing.

I think the "magic number" is about 4 ppm FC at 30 CYA. While I may drop below 4 ppm during the afternoon, by 9PM I have the FC back to 6. I'd go a couple of weeks at an 8 nightly target (I went 3 weeks) then eased it back to 6.
 

Holydoc

Gold Supporter
Jul 17, 2016
418
Navarre/FL
That is definitely the nice thing about a SWG pool. I do not have to worry about my pool water FC fluctuating. I run my pump 24/7 with my SWG set at 30%. This keeps my FC hovering around 9.5 for a CYA of 70.

Notice that for a SWG at CYA = 70, the minimum FC=3, Recommended = 5, and SLAM =28. So why do I keep mine around 9.5? Because it is not harmful below SLAM levels; it is not high enough to cause any harm to any equipment or people; and it basically guarantees that I will never dip below the minimum FC and will never get Algae. I mean... why hover around the minimum and take a chance?

All that to say, don't chance getting algae by staying right on the edge of the minimum. You basically have a lot of room to breath in the FC range. Use it.
 
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red-beard

Gold Supporter
May 27, 2019
553
Houston, TX
I took the HOCL vs FAC & CYA chart and added a Mustard Algae line. It has been suggested that 0.070 is the HOCl value to prevent Mustard. I say suggested, because it isn't as tested as the 0.050 line for Green Algae. For a CYA of 30, the 0.070 translates to 4.3 ppm FC. Note the 3.3 FC line corresponds to 30 CYA and the Green Algae line.

The issue with Mustard, if the 0.070 HOCl is correct, is the minimum FC becomes 5.8 at 40 CYA. At 50, it becomes 7.1. If your daily FC loss is around 3 ppm, then you should be starting around 7-8 with a CYA of 30, 9-10 for 40 and 10.5-11 for 50.

This is why I started with 30 CYA and a nightly FC of 8 ppm. I think reducing to 6-7 ppm is fine once you've had several weeks without an outbreak, as at least 75% of the day is above the 4.3 ppm value. Again, nightly additions so you have 12 hours at maximum FC.

FCL & sanitization.jpg
 

goofiness

Bronze Supporter
LifeTime Supporter
Jul 3, 2011
75
Stockton, CA
Thanks to all for the info, advice. Because I have some difficulty carrying jugs of bleach out to the pool, I was hoping to be able to reduce the volume needed every evening, not necessarily to save a few dollars, but to save my back, hip, etc. So, for me, it is not much different needing to add 42 oz or 56 oz, to get to FC of 7 vs. 8. I may try letting my guard down a little, and seeing what happens if I go for minimum FC of 5. I add at 8PM, and the pool is not in the sun until around 9AM. So, I get around 13 hours of FC 8.

Also, I'm still cautiously adjusting my CYA level. I got 40 two weeks ago, but last Sunday my wife, and I, only got around 35. I'll test again, then decide whether to add more. After I SLAMmed, the CYA dropped to 0; what a surprise!

Anyway, for now, I'm OK, and thanks, again, for all the replies.
 

red-beard

Gold Supporter
May 27, 2019
553
Houston, TX
Like Ben Kenobi, "We must be cautious."

Having fought this battle for YEARS, this is the first year I've had the mustard under control. 6 FC every night and 30 CYA works. Try 5.

What is your FC in the evening? How much are you losing?
 

goofiness

Bronze Supporter
LifeTime Supporter
Jul 3, 2011
75
Stockton, CA
Red Beard, thanks. Evening FC around 6, AM around 8. Loss of 2ppm, or 25%, pretty consistent with CYA at somewhere between 35-40. I think I'll leave it as is, since I'm in a regular routine, adding 2ppm worth of bleach every evening. Once the season advances, and there is less sun exposure, the evening FC should creep up, and maybe I can drop the min and targets a bit.