New pool owner - learning to remove mustard algae, now chlorine levels are zero

[Lugnut2683]

Hey everyone,

I'm a relatively new pool owner (9 months) and have a 14,500gal in-ground pool/spa. I've never had any issues with my chemical levels (tested weekly) until I recently started seeing mustard algae growth after a few birthday pool parties (in September and October). My kids also brought dirty/sand/saltwater body boards into the pool which I also suspect contributed to the recent algae growth.

To combat the algae, I started with raising chlorine levels, which didn't work. I then tried Clorox algaecide, which worked for a short time, but then the algae returned in full force.

After these initial attempts, I then removed and cleaned all of the pool filters, replaced the pool cartridge filter, increased chlorine levels, started brushing with a stainless steel brush (as opposed to nylon), and used "Yellow Treat" along with aglaecide and additional chlorine. The algae is nearly gone, most of which I credit to the stainless steel brush helping to remove it from the textured pebble/plaster floor.

However I still see slight staining and a few slightly yellow areas in the dark corners of the pool, and I'm having difficulty raising the chlorine levels. I've been using a Clorox shock product and even after adding, I barely get a reading on free or combined chlorine.

Where should I start? My CYA levels are not high and all other levels seem within range. Is my CYA level perhaps too low? Photos attached for reference.

I have a lot to learn but I appreciate your help!

EDIT: after doing some more reading, I've already ordered a Taylor K-2006C test kit, so stay tuned for results.

 

[Bperry]

Hey everyone,

I'm a relatively new pool owner (9 months) and have a 14,500gal in-ground pool/spa. I've never had any issues with my chemical levels (tested weekly) until I recently started seeing mustard algae growth after a few birthday pool parties (in September and October). My kids also brought dirty/sand/saltwater body boards into the pool which I also suspect contributed to the recent algae growth.

To combat the algae, I started with raising chlorine levels, which didn't work. I then tried Clorox algaecide, which worked for a short time, but then the algae returned in full force.

After these initial attempts, I then removed and cleaned all of the pool filters, replaced the pool cartridge filter, increased chlorine levels, started brushing with a stainless steel brush (as opposed to nylon), and used "Yellow Treat" along with aglaecide and additional chlorine. The algae is nearly gone, most of which I credit to the stainless steel brush helping to remove it from the textured pebble/plaster floor.

However I still see slight staining and a few slightly yellow areas in the dark corners of the pool, and I'm having difficulty raising the chlorine levels. I've been using a Clorox shock product and even after adding, I barely get a reading on free or combined chlorine.

Where should I start? My CYA levels are not high and all other levels seem within range. Is my CYA level perhaps too low? Photos attached for reference.

I have a lot to learn but I appreciate your help!

EDIT: after doing some more reading, I've already ordered a Taylor K-2006C test kit, so stay tuned for results.

Once you get the kit. Post your results here. You can toss the strips away, they are pretty worthless.

How much of the “yellow treat” did you add? That is bromine and not good to put in pool water as it’ll convert your pool to bromine instead of chlorine. Don’t add any more. The Clorox chlorine also usually has copper in it which will stain the pool, so you should consider ditching that stuff. Once you get accurate test results, someone can advise further.

Mustard algae is extremely rare and so I’d suspect you have have normal algae caused by low chlorine combined with high CYA.

 

[Newdude]

+1. If the pool is properly chlorinated, it can handle any boogie board (etc) from the beach you bring back. Everyone always likes to assign a contributing factor, but it's always low FC per the CYA level that was to blame.

And Welcome !!!

Read up and ask away : Pool Care Basics
Download : PoolMath
Follow : FC/CYA Levels
Witness : Test Kits Compared

And from now on, only chlorinating liquid from the pool aisle or bulk supplier. Pretty much all other chlorines/bleaches will jack something. CYA (pucks), CH (powder shock), foam and suds (household bleach) or copper (4 in 1 / anything that says blue on the labels / many algecides).

So chlorinating liquid, muriatic acid, and maybe 20 mule team borax. Don't add anything else if it's not approved here.

 

[Lugnut2683]

Wow thank you guys! I admit that there was a period of time (roughly 2.5 weeks) where I was out of town and did not chlorinate the pool and allowed the levels to drop to zero, probably initiating the growth.

Regarding yellow treat, I've only put in about 3 capfuls over the course of 3 weeks, but I did read up about converting your pool to bromine... according to the test strip there is no bromine reading but I will post better results once I get the test kit.

Regarding copper staining... is there a remedy for that if that turns out to be the case? There are some areas at the bottom of the pool that I brush and still have a slightly yellow/green tint to them.

Lastly - I have gloss black tile along the water line that has started to turn white. I frequently use strong muriatic acid and a brush to combat this, but it's at a point where it seems stained and straight muriatic acid won't do the job. Is there a method for clearing cloudy gloss black tile?

 

[Bperry]

Wow thank you guys! I admit that there was a period of time (roughly 2.5 weeks) where I was out of town and did not chlorinate the pool and allowed the levels to drop to zero, probably initiating the growth.

Regarding yellow treat, I've only put in about 3 capfuls over the course of 3 weeks, but I did read up about converting your pool to bromine... according to the test strip there is no bromine reading but I will post better results once I get the test kit.

Regarding copper staining... is there a remedy for that if that turns out to be the case? There are some areas at the bottom of the pool that I brush and still have a slightly yellow/green tint to them.

Lastly - I have gloss black tile along the water line that has started to turn white. I frequently use strong muriatic acid and a brush to combat this, but it's at a point where it seems stained and straight muriatic acid won't do the job. Is there a method for clearing cloudy gloss black tile?

Let’s get all your chemistry straightened out before messing with the calcium scale on the tile. It’s just cosmetic but the other stuff can do multiple bad things. Don’t add anything else other than liquid chlorine until your test kit arrives.

And those strips really are meant for the garbage can. We don’t believe anything they say as they’ve been proven wrong so often in the past.

 

[Lugnut2683]

Alright guys, moment of truth. I just got back from being away for 5 days so my pool chemistry is sad at best (results are from using the Taylor test kit):

Free chlorine - basically 0 (couldn't get a reading)
Combined chlorine - 0.2
PH - was super low (orange), did base demand test, added 12 drops 0006 to bring it to 7.4
Alkalinity - 5 drops 0009 = 50 ppm CaCO3
Calcium Hardness - 55 drops = 550 ppm CaCO3
CYA: photo says it all (way high)

So what is the first step here?

 

[Bperry]

Alright guys, moment of truth. I just got back from being away for 5 days so my pool chemistry is sad at best (results are from using the Taylor test kit):

Free chlorine - basically 0 (couldn't get a reading)
Combined chlorine - 0.2
PH - was super low (orange), did base demand test, added 12 drops 0006 to bring it to 7.4
Alkalinity - 5 drops 0009 = 50 ppm CaCO3
Calcium Hardness - 55 drops = 550 ppm CaCO3
CYA: photo says it all (way high)

So what is the first step here?

1. Only test chlorine with the 10ml sample.(you don’t need 0.2ppm accuracy and you waste reagents boing it)
2.Add 5ppm of chlorinating liquid
3. You can use borax to raise the pH

 

[ajw22]

With your CYA over 100 you need to lower your CYA to around 70 by draining your pool or doing a water exchange.

Draining - Further Reading

www.troublefreepool.com

No point in throwing chemicals into water you are going to drain.

Drain and refill your pool then get your FC up around 8 and check your pH and TA.

 

[Bperry]

With your CYA over 100 you need to lower your CYA to around 70 by draining your pool or doing a water exchange.

Draining - Further Reading

www.troublefreepool.com

No point in throwing chemicals into water you are going to drain.

Drain and refill your pool then get your FC up around 8 and check your pH and TA.

Whoops, didn’t see the CYA number.

 

[Lugnut2683]

Hey everyone, checking in after doing a partial drain/refill (about 1/4 of my 14,400 gal pool). I know that I probably should have drained my pool more considering the high CYA levels, but I wanted to see where the levels are at with a partial drain/refill. So here are my current test results after refilling and adding 2 gal of liquid chlorine (chlorine was added on 12/20/23 - Wednesday):

FC = 2.5 ppm (yay! I couldn't get chlorine readings before)
CC = 1 ppm
PH = 7.0 (I added 6 drops of base demand R-0006 to get it to 7.4)
TA = 80
CH = 160
CYA = 90

So what are the recommendations of my fellow experts? I'll continue to test daily as I presume the still high CYA will affect my FC/CC levels. If I need to drain more I will. Obviously PH needs to be raised as well.

 

[ajw22]

Your pH is fine. With a TA of 80 just let your pH rise naturally.

Your CYA is still too high if you intend to follow the SLAM Process and clear your algae problem.

 

[Newdude]

I know that I probably should have drained my pool more considering the high CYA levels,

Multiple drains become counter productive because you drain good water with the bad, with diminishing returns. Two half drains nets 100% of the volume but a 75% exchange, for example.

I'll continue to test daily as I presume the still high CYA will affect my FC/CC levels

Here ya go for whatever stage it's at along the way. Screenshot or download it to your phone pics and it'll always be one click away in your pocket.

 

[Lugnut2683]

Thanks for the info guys - it's clear that I need to drain and refill here to get my CYA down once and for all. I will begin that process this week and report back.

 

[Lugnut2683]

Drained! Took the opportunity to also pressure wash the walls and get the last bit of mustard algae that was remaining. Now refilling and adding liquid chlorine. Will post test results once pool is full...

 

[Newdude]

Glad it went well.

 

[Mdragger88]

Looks like a great opportunity to clean under the drain covers & in the light niches if you have any.

 

[Lugnut2683]

So I completed the pool refill on Tuesday Jan 2nd. Added 2 gal of liquid chlorine and tested the next day (Wednesday Jan 3rd):

FC = 0.5
CC = 0
PH = 8+
TA = 120
CH = 50
CYA < 30

Based on these results, I added an additional 3 cups of liquid chlorine and 2.5 cups of muriatic acid (on Wednesday Jan 3rd). Then tested this morning (Friday Jan 5) and my results are as follows:

FC = 0
CC = 0
PH = 7.4
TA = 140
CYA < 30

So it looks like my chlorine levels dropped, so I will add additional liquid chlorine tonight. Am I being too timid with my initial chlorine addition? Any other recommendations?

 

[mknauss]

Add 30 ppm worth of CYA. The FC is disappearing as you have no stabilizer in the water.

 

[proavia]

There may be some residual algae as well.
Test FC daily and dose as needed.

How much stabilizer did you add right after the initial fill?
Is the CYA test the least bit cloudy or is it clear?

Also consider an Overnight Chlorine Loss Test.

 

[Lugnut2683]

I did not add any stabilizer after the initial fill. Would using the Clorox shock product I referenced above be ok to both raise chlorine and CYA levels? Once stabilized, I plan to only use liquid chlorine.