Is this black algae or needing new marcite?

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R

reed410

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Jun 28, 2024
8
Detroit/MI
Long story short, we are in the midst of opening a pool that hasn’t been in the best shape after not being opened in 2022. 2023 was spent fighting to get chemicals right after not draining. I have a suspicion that it needs to be remarcited (don’t remember the last time it was) and am questioning whether the dark spots on the cement (see attached) is an indication of needing marcite or if it’s a bad algae problem. The chlorine has been 10+ ppm but the cya may be affecting things at 100+. We had a slow start this year after a hot May and a new mesh cover that probably caused a swampy pool from what I’m gathering. Two rounds of floc and shock have gotten us this far, but now the issue is the cement sides. The dark will not scrub off as I have tried and tried to no avail. Pool businesses around me have been no help, just want me to dump money down the drain literally. Please advise and thank you in advance. Hopefully someone can tell from these pictures.
 

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reed410 said:
a new mesh cover that probably caused a swampy pool from what I’m gathering
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Mesh covers do not cause a swampy pool. Opening late, allowing water temps to rise above 60, without sanitation causes the swamp.

Get in the pool and see if you can scrape some off, then wipe on a paper towel. Bamboo skewers work well too.

If it smudges Black or Green on the paper towel, then it is probably black algae. If not, likely a plaster problem.
 
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Just trying to rule out copper stains. See if this article helps at all.

www.troublefreepool.com

Stains in Your Pool

The stained pool is beyond embarrassing. Our in-depth Guide to remove stains in your pool will help you to remove the stains and prevent them in the future.
www.troublefreepool.com www.troublefreepool.com

www.troublefreepool.com

Pool Care Basics Archives

Your one-stop shop for all things TFP to include: ABCs of Water Chemistry, Recommended Chemicals/Levels, Test Kits, Troubleshooting, and much more!
www.troublefreepool.com www.troublefreepool.com
 
We may be able to provide better advice, but we will need to see a full set of test results from your own TFP recommended test kit. The second link above will take you to an article regarding the test kits.
 

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Probably not related to why you're here, but to best manage your FC, you need the accuracy of the FAS/DPD Free Chlorine Test. This kit will provide accurate FC results up 50 ppm with precision from 0.20 to 0.50 (depending on sample size). The reagents come with the K-2006/K-2006C kits.

The better deal is to buy the (larger size) reagents only Here and Here.

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Thanks for the feedback. I finally got a fas/dpd test. FC is a whopping 18.5. CC is 1. The cya is high at 140 because we used dichlor granular not knowing it had cya. Looks like we have chlorine lock. Don’t really want to partially drain the pool this late in the season but that might be my only solution. Any other thoughts would be appreciated.
 
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