Black algae or something else?

[alkis_7]

Hello guys from Athens, Greece.

We have a pool for the last 10-12 years in our home. It’s an overflow pool, with about 100 cubic meters of water.

We have a problem of black stains in the side and the bottom of the pool, between the tiles. The chlorine and pH levels are always at the right spot (~2.0 ppm of chlorine, 7.2 to 7.4 pH), we do a weekly maintenance vacuuming and brushing the pool and the water recirculating 12-15 hours daily. These stains tho keep staying there for the last 4-5 months. I think it’s black algae but do you have any other idea? How can I get rid of these without emptying the pool?

Thank you so much for your help.

 

[Bperry]

Hello guys from Athens, Greece.

We have a pool for the last 10-12 years in our home. It’s an overflow pool, with about 100 cubic meters of water.

We have a problem of black stains in the side and the bottom of the pool, between the tiles. The chlorine and pH levels are always at the right spot (~2.0 ppm of chlorine, 7.2 to 7.4 pH), we do a weekly maintenance vacuuming and brushing the pool and the water recirculating 12-15 hours daily. These stains tho keep staying there for the last 4-5 months. I think it’s black algae but do you have any other idea? How can I get rid of these without emptying the pool?

Thank you so much for your help.

Welcome, it does look like algae which is an indication of too little chlorine. Do you have a way to test for CYA? Here’s a chart showing the correct amount of chlorine needed depending on how much CYA is in the water.

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.

www.troublefreepool.com

 

[Mdragger88]

As @Bperry mentioned, the answer is more chlorine.
How are you currently chlorinating the pool? (Cal hypo, trichlor, dichlor, liquid chlorine or salt water chlorine generator?)
You can show us the package label ingredients list if you’re unsure.
Along with righting the ship with adequate fc levels here’s the black algae guide

Black Algae

This guide provides a step by step procedure for eliminating black algae in your concrete or gunite pool. Read full post here.

www.troublefreepool.com

And have a read of the Pool Care Basics

 

[alkis_7]

Thanks for your answers guys.

So, we have a salt chlorinator to chlorine the pool. I think it’s a BSV model, if I remember correctly. Once a month in the summer, we use dichlor to boost the chlorine levels cause of the heat and the high temperatures.

I think I can check the CYA via PoolLab 2.0 that we use to check the chlorine and pH levels. Is it reliable for such a measurement? If yes, I’ll do it tomorrow morning and I’ll come back with them results.