Light spread of black sediment

[RonPace]

I am quite proud of the pool this year having learnt lots of tricks here.

Last week though, the pool had no use so the water was not being churned other than from the return jets. I guess as a result, I have a very light spread of black sediment. It is so fine that when I even go near it with a brush, it swirls into a green cloud and dissipates into the water.

Whatever it is, it just goes straight through the filter when vaccd into it. I tried sweeping it ever so gently into a corner, but most of the stuff disappears, leaving clear water, only to return the next day!

Is this algae? Can one get rid of it successfully, or is it just a case of brushing the pool every day? Talking to others, I get answers of this product and that product, but having got the pool running quite nicely with hydrochloric acid and diluted bleach (in France, Javel) and rid of all the fancy cans on the shelf, I am hoping for a simple solution...

Current readings
Salt 3.6
TC 5
FC 4.5
Ph 7.7
TA 90-100
CYA 67

[RonPace]

Reading the stickies above, mine is live algae, or sounds like it.

How sensitive is the CYA to Chlorine relationship? My CYA is mid sixties, but a quick look at the chart shows that this is a bit low and that it should be 70 - 80. would a difference of 10 to 15 ppm be significant? And the reason for this black/green dust?

[Teapot1]

Hi Ron, sometimes the black/brown is oxidised stuff. I have put this under the microscope and its not (in my case ) algae but very fine dust from the fields nearby being cut.
What I do is put a cotton tea towel into the skimmer and it collects it nicely.