Yellow algae not dying

[jfricker]

Hello - I have yellow stains on the bottom and sides of my pool that I think is yellow algae. I recently neglected the pool and FC was zero, and leaves are falling in the pool, and lots of rain, etc... The yellow is mostly on rough splotches of plaster, and more on the shaded areas of the pool - the rough areas started showing up shortly after a new plaster job 7 years ago.

I have the TF100 test kit and have been using bleach for several years. Before I started the mustard algae super SLAM recommended here, I back flushed my sand filter and my pool numbers were:
FC - 6.5
CC - .5
PH - 8, so I added muriatic acid to lower it to 7.5
CH - 225
TA - 90
CYA - 40
Borates - 40ish estimated, I have not measured that for a few months

The chart recommends I bring FC up to 23.8 for yellow algae. I went up to 27 and brushed and pulled the light fixture and brushed in there too. After 5 hrs it was 25, and then overnight it dropped to 23. I added a bit more bleach bringing FC up to 26.5 (29 hrs into process), and did more scrubbing and 1 vacuuming. Overnight FC dropped to 23 and CC was zero, then by evening FC was 22.5 (so it dropped .5 during the day). The pool has had FC above 22.5 for 54 hrs, and when I scrub the yellow spots, they remain yellow. I have been running my sand filter 24/7 with a cup of DE on top and the water is very clear now.

I did use a dose of copper algaecide a week ago with no effect. I know that was a no-no after reading up on yellow algae here.

Any suggestion are appreciated!

John Fricker

 

[duraleigh]

Your description fits mustard algae to a T except for one thing......it apparently is not brushing off. Mustard should be almost dust-like and "whoosh" away when you brush it.

Got a pic? Can you confirm it does not brush off?

 

[Texas Splash]

John, I would also ask you to consider letting the FC fall to 16 based on your CYA of 40. There's no need to be at such a high FC level for so long. You'll just waste bleach. If you look at the Pool School - Mustard Algae page, it states to perform a standard SLAM Process first, making sure to pass all 3 criteria "before" increasing the FC to MA levels and then only for 24 hours. After that, you may require an elevated FC level to some degree if the staining is organic, but if it's not, the higher FC level probably won't help anyways. The roughness you described almost seems like you may have a scaling issue to contend with as well huh?

The roughness started some 7 years ago. How long ago did the staining start? Just this season or well before?

 

[JamesW]

It might be iron. Try some vitamin C on a spot.

 

[jfricker]

Thank you for the suggestions. I'll take a pic and post it, but it might be a day or two for me to be home during daylight to get a pic. I have brushed the yellow spots a number of times and they do not woosh off.

The rough splotches appear to me to be a result of a poor replaster job. The rough patches are where the smooth plaster looks like it was etched with acid, so they are rough, like 80 or 120 grit sandpaper, which is great for growing things to hang onto. The rough patches started showing up a few months after the replaster in 2011, and have slowly gotten bigger (more area, not really deeper or rougher). The mustard algae only showed up a few weeks ago. Elsewhere in the pool I have concretions growing, but the etching and concretions are separate from mustard algae. I do regularly add muriatic acid (~ once a month) as my pH drifts up slowly over time.

I misunderstood I was supposed to complete the SLAM before starting the mustard algae process. In any event, I have used about 6 gallons of bleach so far in the process and the FC level remains pretty high, so the chlorine is not working very hard.

I'll try some Vitamin C.

Regards,
John

 

[jfricker]

Thank you for the suggestions. I'll take a pic and post it, but it might be a day or two for me to be home during daylight to get a pic. I have brushed the yellow spots a number of times and they do not woosh off.

The rough splotches appear to me to be a result of a poor replaster job. The rough patches are where the smooth plaster looks like it was etched with acid, so they are rough, like 80 or 120 grit sandpaper, which is great for growing things to hang onto. The rough patches started showing up a few months after the replaster in 2011, and have slowly gotten bigger (more area, not really deeper or rougher). The mustard algae only showed up a few weeks ago. Elsewhere in the pool I have concretions growing, but the etching and concretions are separate from mustard algae. I do regularly add muriatic acid (~ once a month) as my pH drifts up slowly over time.

I misunderstood I was supposed to complete the SLAM before starting the mustard algae process. In any event, I have used about 6 gallons of bleach so far in the process and the FC level remains pretty high, so the chlorine is not working very hard.

I'll try some Vitamin C.

Regards,
John

I took a couple pics, but they don't show the yellow well. I probably need to take them with the sun overhead. The pic with the brush also has dark live oak leavs and one acorn in it. The average yellow spots have a diameter half the leaf length. This evening the FC was 19.5 and CC was zero, so FC has dropped 3 ppm in 24 hrs without adding additional chlorine.

Thanks,
John

 

[JamesW]

I'm thinking iron. Did you try vitamin C?

 

[ping]

I'll suggest that you might want to use a stainless steel brush.

 

[duraleigh]

Identify the stain. Then, folks will have a suggestion on how to get rid of it and how to prevent it. Identify the stain.

 

[jfricker]

I have not yet tried vitamin C, but I will. I'll also try a SS brush. How do I identify the stain?

Thank you,
John

 

[JamesW]

I think that it's probably iron. If vitamin C clears it, it's iron.

 

[duraleigh]

Pool School - Metals in the Water and Metal Stains. I agree that it's likely iron but PLEASE identify the stain before you apply treatment (like an SS brush that may NOT be necessary). Identify the stain, then treat for removal and prevention.

 

[jfricker]

Pool School - Metals in the Water and Metal Stains. I agree that it's likely iron but PLEASE identify the stain before you apply treatment (like an SS brush that may NOT be necessary). Identify the stain, then treat for removal and prevention.

I tried the vitamin C test and it is inconclusive. In the pic below, I placed two acorn caps below two splotches that were yellow that I did the vitamin C five minute soak on. They look a little less yellow, but maybe because they got scrubbed by the sock in the process.

In the photo below, I put the sock on the darkest park of the yellow ring, right under the acorn cap, and can not tell a difference in yellowishness.

I tried a small SS brush on a spot and it definitely cleans it up, after the cloud of plaster floats away.

 

[JamesW]

Hard to tell for sure. Maybe iron, scale or algae.

I would add a metal sequestrant and brush the spots off. Then, be careful to maintain good chemistry.