Mustard Algae? Or chemical stain?

[Vtattebury]

<<photos sent to poolforum acct.>>

Last year I had a localized stain (about 6'x3') downstream of the outflow where I put most of my chemicals in. I thought I had stained it by some undissolved chem's settling on the bottom, but now (this year) I have the same color ring around the top of the pool, and a couple more small areas of a similar stain. I've tried to brush it and it doesn't change appearance at all (someone mentioned Mustard would initially come off, but return the next day...this stuff doesn't change at all after brushing).

Original stain doesn't seem to be "growing" per-se, just appearing in different areas.

Any ideas? My one checmistry issue is high stabilizer (CYA about 90), so I know my shock level needs to be higher. Using Ben's best guess pool chart, I shock at around 25, and was able to maintain this level for many days this season (I had to open the pool early due to some yard construction, and it was way too cold to swim, so I let it stay in shock mode for quite awhile).

Water is otherwise clear, virtually no CC.

Typical day's measurements:
FC 8-10
CC < .5
TA 40-50
CH ??
CYA 90
PH 7.4-7.6 (keeps dropping maybe due to Acidic NJ rain?) Also trying to elevate the TA to settle the swings.

I use mostly BBB method, but use trichlor tabs for maintenance since I'm out of town a lot.

Vinyl liner
30x15 above ground
Swim pro sand filter
Hayward 1.5 HP power flo matrix pump
Using the recommended test kit

[swimdaddy]

If it doesn't come off, than you may have some type of metal in your pool staining your liner. Its a pretty common problem. Is your pool water municipal or from a well? Ground water tends to have more minerals in it and can stain you pool. My in-laws, bless their hearts, use a copper based sanitation system in their pool and they get similar stains along the water line. Can't convince them to switch to BBB.

[polyvue]

Can't see the photos, of course. If that's important, consider putting them on imgur or another photo site and give the link.

swimdaddy may be right if the make up water is coming from a well or if the pH has been much lower in the past and there is copper to be had (heater?)

But I would guess algae, species undetermined. If it's mustard algae, you'll be in a world of sorrow trying to contain it with CYA of 90 or more. That's nearly unmanageable-- you'll be carting in bleach by the truck load to fix it. Better to to get that CYA down by several controlled partial drains of the pool -- I have a gunite pool and do 20% drain and refill but you'll have to determine what is safe for your pool.

Yup, trichlor is convenient but that's what got you here! I'd recommend trying to reconfigure your schedule so you can start dosing with bleach and reserve the trichlor for very long trips. There's no calcium in the pool? I'd definitely get the alkalinity up to 70-80 ppm or so, you need some pH buffering.

The trichlor is likely contributing to pH decline. What are you using to get it back into range? Sodium carbonate? Borax?

[swimdaddy]

Agreed, seems like the 2 most common causes of algae blooms are sanitizer to low or stabilizer to high.

Forgive me for my ignorance, I am still learning, but if it were mustard algae, wouldn't it scrub off, or scrape off with a fingernail?

[polyvue]

Agreed, seems like the 2 most common causes of algae blooms are sanitizer to low or stabilizer to high.

Forgive me for my ignorance, I am still learning, but if it were mustard algae, wouldn't it scrub off, or scrape off with a fingernail?

Hi swimdaddy,

Yes, I thought as much but I've seen black algae so embedded in a wall that not even a metal brush can dislodge it. Also read accounts of mustard algae, often described as powdery and easily scattered like a cloud of dust but keeps coming back. I can only share my very recent experience which may or may not be relevant. (This is a slow forum, so why not?)

Nine years of pool ownership and I thought I would never see an algae outbreak in my pool ... but it happened for the first time this year. I'm not an expert on types of algae but I'm fairly practiced in its eradication (in other people's pools, of course. ) When you see pool water that is not as reflective as usual or has a slight green or greenish-blue cast, or a surface (skimmer wier or pump basket, a shallow step or return jet) that feels a bit slippery to the touch, then the diagnosis is easy. Some type of green algae is spreading rapidly. But other forms are less obvious in their approach.

My 9-year boast came to an end last month for many of the same reasons other pool owners get into trouble: a combination of factors that included the encroachment of large trees that littered the pool with insects, a dirty cartridge filter, extended periods of low chlorine, and general neglect that extended to failing to brush the pool as frequently as I had in the past, and the gradual aging of equipment (rough surfaces, loose fittings). I knew chlorine demand had been increasing over the months but I didn't take any corrective action.

First sign was how annoyingly difficult it was to keep the spa clean. Then I had to acknowledge that the marcite plaster wasn't as vanilla-frosting white as it had been. Soon after I recognized black algae (spots) in the crevices of the tile in a few locations around the pool... challenging but doable with a SS brush.

I tried to remove a very slight "stain" (it looked like rubbed-in yellow brown dirt) that on closer inspection seemed to be everywhere but was most apparent in the deep end (shaded area). Lots of scrubbing and bleach and it didn't even fade much less disappear. It comes close enough to the description of mustard algae—it could be a different species, I don't know, but it motivated me to action.

Increased chlorine demand, coupled with perfectly clear water and a growing generalized discoloring of the walls and floor that wasn't a metallic stain. Hanging over the side of the pool, I could see that if I focused on a tiny area I could just manage to clear a spot with great effort and a tri-chlor tab.

Anyway, this wasn't meant to become the novel that it has become. Since then, I have done all the things I should I have done earlier this year: cut back the trees, cleaned the filter, brushed the pool, increased filter time 25%, experimented with shock regimens—low pH ~7.2 to 7.5 with large and frequent applications of fresh (date-selected) 10% sodium hypochlorite works as advertised! I think I was up to 70% of CYA for a while. At CYA of 35-40, I'll swim when FC is less than 12 ppm so that's my new target maintenance level.

I waited far too long. I'm actually replacing the plastic fittings that can't be made right after soaking in a bucket of 5% bleach all day and then scrubbed. Main pump filter basket, two eyeball returns and a float for the automatic pool sweep, so far. I haven't yet pulled out the light niches but that's next. Just hope that judicious applications of chlorine will disarm anything growing inside the PVC pipes. But the pool looks almost like it did when I first filled it in 2007. 🙂

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I think everyone who owns or is responsible for a pool is still learning. There are just too many fields of knowledge required for any one individual to know everything... plumbing and hydraulics, electrical, chemistry, materials science, etc.

[swimdaddy]

Thanks, I think that helps, shared testimonials are very helpful!