Sanity check - is this mustard algae?

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H

HudsonValley68

Member
Jun 22, 2024
20
Wappingers Falls, NY
Pool Size
21000
Surface
Vinyl
Chlorine
Liquid Chlorine
Hi all! I've had a lot of success on the first few months of our new (to us) pool thanks to the forums, test kit, and following 'the plan' here.

A couple of weeks ago, some green-ish spots started appearing on the 'angles' of the pool as well as in the shallow end. It looked like algae to me and I started SLAMing. I am not at home 7 days a week, so keeping up with it is difficult but I've leaned into putting a little too much liquid chlorine in before I leave for a few days and letting it dip back to SLAM level on it's own.

After reviewing the forums I started to think that I have mustard algae, so I added LC to get to the Mustard-level of FC in the pool last night. I've been running the pump 24/7 as prescribed. This morning I noticed that it has not changed the spots at all. I am now doubting whether it is algae. It doesn't move 'like sand' it cannot be brushed away. It has come and gone in the few months the pool has been swim-able, so I know it's not permanent.

Please take a look at these pics and help me understand what I'm dealing with. I'm going to go broke going nuclear with the cost of LC additions that don't appear to be working!

My maintenance logs and tests are in my profile. THANKS!

August 20: I think I had a camera filter on - the images from Aug 21 are more color accurate

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August 21:

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It's not grainy and does not 'rub off'. Brushing does not move it or reduce it. It has come and gone before, but never 100% gone. I originally thought the remnants was staining (old pool left closed for 4 years) because the liner is very old and needs replacement.

You'll see on my Pool Math history that my last OLCT was Aug 20 evening @ 21 FC and Aug 21 morning @ 19 FC. Not a 1ppm change but 2ppm.
 
A loss of 2ppm does usually mean algae so maybe that is what it is and it’s just not completely gone yet. People on here say mustard algae is rare, but is difficult to get rid of unless you go real strict with a slam. So my guidance would be to continue u til your slam is complete and be sure to do a mustard algae slam where at the end you raise the chlorine past the regular slam.
 
kul said:
A loss of 2ppm does usually mean algae so maybe that is what it is and it’s just not completely gone yet. People on here say mustard algae is rare, but is difficult to get rid of unless you go real strict with a slam. So my guidance would be to continue u til your slam is complete and be sure to do a mustard algae slam where at the end you raise the chlorine past the regular slam.
Click to expand...
Thanks. I've been following that regiment, but because it's not clearing up yet and cannot be scrubbed / moved I'm doubting myself and whether it really is mustard algae.
 

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Mdragger88 said:
Follow the instructions in the link @PoolStored posted after you complete your ma 24 hrs.
Did you have alot of leaves in the bottom of the pool upon opening?
Click to expand...
I will!

The pool was left closed with safety cover for at least 3-4 years. You could not see more than about 2" deep - totally black. The pool company did FLOC & Shock with a few vacuum to waste (with their own pump) in between treatments over a 6 week period. Never ran our pump or filter until they "finished the job" and the water was clear. So I doubt there was debris in the pool, but it was a mess.

The first time the pool pump was turned on the pressure was about 23psi so I know they lied when they said they cleaned the filter. It was a great feeling to see proper circulation today!
 
HudsonValley68 said:
The pool was left closed with safety cover for at least 3-4 years. You could not see more than about 2" deep - totally black. The pool company did FLOC & Shock with a few vacuum to waste (with their own pump) in between treatments over a 6 week period. Never ran our pump or filter until they "finished the job" and the water was clear. So I doubt there was debris in the pool, but it was a mess.
Click to expand...
They are likely organic stains. Follow the stain guide...
 
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These spots went away and came back a few weeks later, so I don't think it is a stain - it's growing and spreading.
There is a stupid amount of chlorine in the pool now. The FC test is tough because it goes from red to a light straw yellow instead of clear.
Unlike last time not only is it not going away the green spots have been spreading.
The water is crystal clear and circulation is great now that I have the filter cleaned, but whatever it is I'm not making progress.
Still losing my mind here!
 
It is likely to be something under the liner that is bleeding through.

Discolouration of Liners | Aquaflex

aquaflex.co.uk aquaflex.co.uk

What causes staining or discoloration of the vinyl below the water line? | McEwen Industries

While all stains are either mineral or organic, the most common cause of staining and discoloration of your liner below the water line is secretions by micro-organisms. As these micro-organisms feed, they secrete dyes, which can be one of many colors that stain the vinyl. Although these stains...
mcewenindustries.com mcewenindustries.com
 
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JamesW said:
It is likely to be something under the liner that is bleeding through.

Discolouration of Liners | Aquaflex

aquaflex.co.uk aquaflex.co.uk

What causes staining or discoloration of the vinyl below the water line? | McEwen Industries

While all stains are either mineral or organic, the most common cause of staining and discoloration of your liner below the water line is secretions by micro-organisms. As these micro-organisms feed, they secrete dyes, which can be one of many colors that stain the vinyl. Although these stains...
mcewenindustries.com mcewenindustries.com
Click to expand...

Yes! I did not know liners are semi-porous. This is indeed a stain issue and not an algae issue.
I'll switch gears and stop dumping expensive chlorine in there.
THANKS EVERYONE!
 
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