Is this the mustard algae I need to worry about?

[joshf]

I'm a relatively new pool owner and have been lucky so far with clear water without any major outbreaks of algae. However, occasionally I'll get some yellow growth/stains in corners, or around the water outlets. In the attached picture, you should see some yellow in the corner, just below the tile. It brushes right away, but will come back. It has never gotten to the point where I can't brush it away. Is this something to worry about - do I need to do mustard SLAM when I see that? I know I've seen much worse on this forum, so don't know if I'm making a big deal out of nothing, or if my stance should be "any sign of algae needs to be taken seriously and killed off".

 

[Richard320]

If it's on the shady side, it could be mustard algae. Otherwise, it's just a low-level algae infestation probably caused by poor circulation and lack of brushing. I suspect you probably could pass an OCLT right now, so there's no point in starting a full SLAM. Be heavy-handed when you add bleach and brush a couple times a day to both loosen the biofilm and improve the circulation of chlorine-laden water in those areas.

I sprung for a corner brush that looks like this. I haven't tried it as a vacuum head.

 

[ajw22]

That looks like normal algae.

Post your test results.

 

[joshf]

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Test Results 05-10-2019 @ 11:19 PM
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Free Chlorine: 4.0
Combined Chlorine: 0.0
pH: 7.6
Total Alkalinity: 80
Calcium Hardness: 375
CYA: 50
Temperature: 76°F
CSI: -0.02

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[ajw22]

Your FC is at the minimum level for CYA 50. You should be keeping your FC at 6-8. See FC/CYA Levels

As Richard suggested keep the FC around 10 for a while and brush those areas a couple of times a day. Once you no longer see the green returning then drop FC down to 8. Make sure those areas are brushed as part of your normal brushing routine.