Unable to get rid of Mustard Algae

TJrubicon

Member
Feb 2, 2021
16
Woodland Hills, Ca
Hi everyone,

Would like to introduce myself as this is my first post on TFP ( long time reader and follower). I purchased a home with a 40,000 gallon plaster in ground pool about 1 year ago. This is my first time owning and taking care of a pool, and thanks to this website I have done a lot of learning, using the BBB method to care for it. I noticed throughout the time I had the pool that during my weekly scrubbing, there I see almost like dirt on the walls and floors which rapidly comes back. I later realized this is mustard algae, as its a dark pool and the color is hard to tell.

For the last 7 days I have been SLAMing my pool, using both the tables and calculators on this website to keep things in balance. Here's the thing, my CYA is 65, so the shock level should be 27ppm chlorine, but at this level, the algae is thriving. I had to raise the chlorine to 50+ ppm to have any effect.

I am scrubbing the walls and floors 2x a day
Checking the chemistry 1x a day using a tailor k2006 kit
Automatic vacuum is running 12 hours a day
I am manually vacuuming each night
Took apart the DE filter 2 times to clean and re-assemble
There is nothing floating in the pool

Today is day 7, and the amount of mustard algae i see is drastically reduced, but still there and flourishing. The overnight chlorine drop test was 0.5ppm chlorine, and there was no CC, but I still see the mustard algae. So My question is what do I do next to get rid of this problem? Continue with the hefty slam process until I do not see any more visible mustard algae? is there anything else I can do?


Also, as an aside, I have switched from liquid bleach to cal hypo. The cheapest bleach I can find is $4.19 for a 12.5% gallon. I am able to buy 73% cal hypo 50 pounds for $92, which converts to roughly 45% cheaper than the liquid. IS there something I am missing? Everyone says that the liquid is much cheaper than cal hypo, but not in my case.

Thanks so much for your time and help!
 

CrystalRiver

Well-known member
Jun 19, 2020
533
Massachusetts
There's no way to get a 65 CYA reading using a Taylor 2006. If it's between the lines, round up. The scale is logarithmic and not human readable between the markings.

Your CYA is 70. That makes your SLAM level 28. Running your chlorine significantly higher than this risks damage to your equipment.

Keep holding the SLAM at 28. Mustard algae is tough to kill, and you are only 7 days in. How often are you testing your chlorine levels? Once a day won't cut it. Your SLAM isn't done until you pass all three criteria - you've only passed two so far.

Watch your CH level and your CSI if you are adding cal hypo, especially in the quantities you're talking about using. Once the CH goes up, the only way to get it down is splash-out or drain and fill.
 

TJrubicon

Member
Feb 2, 2021
16
Woodland Hills, Ca
There's no way to get a 65 CYA reading using a Taylor 2006. If it's between the lines, round up. The scale is logarithmic and not human readable between the markings.

Your CYA is 70. That makes your SLAM level 28. Running your chlorine significantly higher than this risks damage to your equipment.

Keep holding the SLAM at 28. Mustard algae is tough to kill, and you are only 7 days in. How often are you testing your chlorine levels? Once a day won't cut it. Your SLAM isn't done until you pass all three criteria - you've only passed two so far.

Watch your CH level and your CSI if you are adding cal hypo, especially in the quantities you're talking about using. Once the CH goes up, the only way to get it down is splash-out or drain and fill.

I had the water tested 3 times and it showed cya of 65 each time. The kit also shows roughly near 70. How many days does it typically take? I feel like 7 days is a long time. I can let the levels dip down to 28, but when I do so, the algae starts growing faster. Testing chlorine once per day.
 

Mdragger88

Bronze Supporter
Jun 1, 2018
1,953
Hernando, Ms
Pool Size
26000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
When doing a proper SLAM Process you test and add chlorine multiple times a day (3or 4 at least) just not more than once per hour.
Also vacuuming & or brushing every day & cleaning your filter when pressure rises 20% over clean pressure. Every hour below slam level FC/CYA Chart gives the algae a foothold that then requires more chlorine. As crystal said - once a day is just playing with it. Only after you meet all 3 end of slam criteria do you then move up to mustard algae fc levels & maintain that for 24 hrs. If you wish to have to maintain a lower fc slam level then you may want to drain some water & replace with fresh to lower your cya. 70 is a bit high if you don’t have a swg. You can always add more cya when the slam is over if you need to. After the 1st few days you may see the fc start to hold longer & you can back down to 2 or 3 times a day. The slam takes however long it takes- there is no magic #-the way to help it along is frequently testing & dosing with liquid chlorine. PoolMath effects of adding will show u the consequence on your ch of using cal hypo . Keep track of that as mentioned above if you wish/ need to use it.
 

TJrubicon

Member
Feb 2, 2021
16
Woodland Hills, Ca
When doing a proper SLAM Process you test and add chlorine multiple times a day (3or 4 at least) just not more than once per hour.
Also vacuuming & or brushing every day & cleaning your filter when pressure rises 20% over clean pressure. Every hour below slam level FC/CYA Chart gives the algae a foothold that then requires more chlorine. As crystal said - once a day is just playing with it. Only after you meet all 3 end of slam criteria do you then move up to mustard algae fc levels & maintain that for 24 hrs. If you wish to have to maintain a lower fc slam level then you may want to drain some water & replace with fresh to lower your cya. 70 is a bit high if you don’t have a swg. You can always add more cya when the slam is over if you need to. After the 1st few days you may see the fc start to hold longer & you can back down to 2 or 3 times a day. The slam takes however long it takes- there is no magic #-the way to help it along is frequently testing & dosing with liquid chlorine. PoolMath effects of adding will show u the consequence on your ch of using cal hypo . Keep track of that as mentioned above if you wish/ need to use it.

What is the benefit of adding and checked 3 or 4 times a day as opposed to having the levels higher than the slam FC such that by the end of the day the level doesn't drop below 28. There's only so much I can do working a 70hr week job.
 

Mdragger88

Bronze Supporter
Jun 1, 2018
1,953
Hernando, Ms
Pool Size
26000
Surface
Vinyl
Chlorine
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SWG Type
Intex Krystal Clear
The higher your fc level the faster it burns off - thus wasting chlorine & potentially damaging surfaces & equipment unnecessarily.
 

Mdragger88

Bronze Supporter
Jun 1, 2018
1,953
Hernando, Ms
Pool Size
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Surface
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We usually suggest starting on the weekend & hitting it hard (testing & adding frequently) -as the 1st couple of days are the worst. Then when u need to go back to work you could test & dose before going to work, as soon as u get home, & then before bed.
The more frequently you test & dose the faster the process will go.
A true SLAM Process is the way to get this really gone. Any shortcuts & you will have just wasted alot of chlorine only for algae to return after a few days or weeks. The idea is that the regular slam fights most of the war then the mustard algae protocol delivers the final blow.
 

Rancho Cost-a-Lotta

Silver Supporter
Apr 10, 2018
1,942
Rancho Cucamonga, CA
I noticed throughout the time I had the pool that during my weekly scrubbing, there I see almost like dirt on the walls and floors which rapidly comes back. I later realized this is mustard algae, as its a dark pool and the color is hard to tell.

I'm just passing through, but are you sure what you're seeing is mustard algae? I'd guess your water temps are in the low 50's and it doesn't sound like you're water is consuming much free chlorine. CCs and overnight chlorine loss are minimal. I'm no expert, but I don't think mustard algae would take hold as quickly as you describe. Is it possible you're just dealing with dirt and sediment from recent winds, or perhaps dead algae? Is you filter large enough to handle the workload? Are you monitoring filter to pressure and cleaning after a 25% pressure rise.

Just a few thought to consider.

Best of luck!
 

TJrubicon

Member
Feb 2, 2021
16
Woodland Hills, Ca
I'm just passing through, but are you sure what you're seeing is mustard algae? I'd guess your water temps are in the low 50's and it doesn't sound like you're water is consuming much free chlorine. CCs and overnight chlorine loss are minimal. I'm no expert, but I don't think mustard algae would take hold as quickly as you describe. Is it possible you're just dealing with dirt and sediment from recent winds, or perhaps dead algae? Is you filter large enough to handle the workload? Are you monitoring filter to pressure and cleaning after a 25% pressure rise.

Just a few thought to consider.

Best of luck!


Thanks for all the feedback. I'm certain it's mustard algae it's responding to the shock and reaccumulating very quickly. It is strange that my chlorine drop test was only 1ppm overnight, I'm just struggling getting the last bits of the algae gone for good. It's been very challenging as it is, can't imagine sitting home and testing every hour. I work 6 days a week. Wondering if there were any other strategies for those of us who can barely keep up with the 2x daily scrub and 1x manual vacuum. Also, ia 4.19$ for 1 gallon of 12.5% bleach a good deal?
 

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TJrubicon

Member
Feb 2, 2021
16
Woodland Hills, Ca
That's a good deal for 12.5% liquid chlorine. I pay about the same at the local pool store for refillable containers.

Ahh great! Glad to know its a fair price.

I checked my free chlorine yesterday pm and it was 51. I will let it drift down to 28, try to sustain it closer to 28 until I can't see any more of this algae, then I will raise it up to 60 per the Mustard algae shock protocol. I will then take apart my filter again and pray to the pool gods this stuff is gone for good.

If this resolves, I will be sure to never let the free chlorine drop below 5. I will keep it between 5 - 10 given my cya of 65.

Thoughts on this plan?
 

mguzzy

Gold Supporter
TJ... Can you fill in your sig with your equipment specs? Its a convenient way for us to reference your setup.

The last phase of a SLAM is always the worst, finding the source of linger algae. Make sure you are cleaning any nooks and cranies where algae can hide. Do you have water features? algae can hide in there, Do you have weird shapes? built-in bar stools that sort of thing? and scrub scrub scrub. Algae forms a protective film over itself and the scrubbing and brushing disrupts that so the chlorine can do its chemical warfare thing. What kind of filter do you have?
 
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TJrubicon

Member
Feb 2, 2021
16
Woodland Hills, Ca
TJ... Can you fill in your sig with your equipment specs? Its a convenient way for us to reference your setup.

The last phase of a SLAM is always the worst, finding the source of linger algae. Make sure you are cleaning any nooks and cranies where algae can hide. Do you have water features? algae can hide in there, Do you have weird shapes? built-in bar stools that sort of thing? and scrub scrub scrub. Algae forms a protective film over itself and the scrubbing and brushing disrupts that so the chlorine can do its chemical warfare thing. What kind of filter do you have?

Ahh will do! Have a variable speed pentair pump, 1 skimmer, 1 main drain, and 2 returns. Its an old pool. It has a 60 size DE filter, no water features, no odd shapes, just a super deep, 12 foot deep end. Wish I could fill the pool and make it all 4 feet or something, 40,000 gallons is hard to care for.
 

mguzzy

Gold Supporter
Perfect.. now stick that in your signature! ;)
I always thought this was just everyone bragging about their pools.. until I started contributing and it really helps when giving advice.

When was your pool built? is it square/rectangular? Algae can hide in the corners. For a pool of that size with one skimmer and 2 returns you might be not be getting enough circulation, What are the dimensions? All this comes into play when trying to deal with algae. If there are only 2 returns depending on how they are situated, there may dead zones that are allowing the algae to grow. My little 20K pool has four returns. So you are going to have to make up the difference by manually moving things around. I know its a lot of pool to brush, but that is what does it. BTW what kind of pool sweep do you have? is it a robot?
 

TJrubicon

Member
Feb 2, 2021
16
Woodland Hills, Ca
Perfect.. now stick that in your signature! ;)
I always thought this was just everyone bragging about their pools.. until I started contributing and it really helps when giving advice.

When was your pool built? is it square/rectangular? Algae can hide in the corners. For a pool of that size with one skimmer and 2 returns you might be not be getting enough circulation, What are the dimensions? All this comes into play when trying to deal with algae. If there are only 2 returns depending on how they are situated, there may dead zones that are allowing the algae to grow. My little 20K pool has four returns. So you are going to have to make up the difference by manually moving things around. I know its a lot of pool to brush, but that is what does it. BTW what kind of pool sweep do you have? is it a robot?
Ahh sounds good will add it to the signature.

It's a large oval pool built in the 1950s. I have the pump running for about 19 hours a day, calculated it to pump 40k gallons per day. I have an irobot mira auto vacuum and then I usually manually vacuum once a week, but during the slam, daily. I want to get this pool to a place where I only check on it a few times per week, although part of me tells me I'll never be able to fully get rid of the algae
 

Mdragger88

Bronze Supporter
Jun 1, 2018
1,953
Hernando, Ms
Pool Size
26000
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@TJrubicon as @mguzzy said be sure to check all crannies- like light niches, ladders& cups, skimmer throats, & weir doors (especially if it has foam).
I had an issue that I couldn’t clear & turned out there was algae in the little diver toy i had been brushing & vacuuming around for a week 😭
 
Last edited:

Mdragger88

Bronze Supporter
Jun 1, 2018
1,953
Hernando, Ms
Pool Size
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Surface
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Ahh great! Glad to know its a fair price.

I checked my free chlorine yesterday pm and it was 51. I will let it drift down to 28, try to sustain it closer to 28 until I can't see any more of this algae, then I will raise it up to 60 per the Mustard algae shock protocol. I will then take apart my filter again and pray to the pool gods this stuff is gone for good.

If this resolves, I will be sure to never let the free chlorine drop below 5. I will keep it between 5 - 10 given my cya of 65.

Thoughts on this plan?
Be sure to use 70 as your cya - u always round up to the next “10” there’s no in betweens. This ensures you’re covered. After you pass all 3 end of slam criteria & then do the mustard algae protocols you should maintain at least the mustard algae fc min (15% of cya) for a while as shown in this chart - so for 70 cya that would be 10.5
 

TJrubicon

Member
Feb 2, 2021
16
Woodland Hills, Ca
Be sure to use 70 as your cya - u always round up to the next “10” there’s no in betweens. This ensures you’re covered. After you pass all 3 end of slam criteria & then do the mustard algae protocols you should maintain at least the mustard algae fc min (15% of cya) for a while as shown in this chart - so for 70 cya that would be 10.5

Thanks for that. How long should I maintain the 10.5?
 

JJ_Tex

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Jul 17, 2019
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The last 24 hours should be the elevated mustard algae shock level. Note, that if I'm reading the chart correctly that should be 40.5 and not 10.5.

The goal here is to give the mustard algae one last zap after you have finished the regular SLAM.
 

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