[amalia (OP)]

Raghu got in contact with us with the following problem:
I have noticed that a black residue settles at the bottom of our swimming pool within 4-5 hours after the pool is cleaned and treated. I notice this especially when the pool gets water from the softner.  Does softened water need a different type of treatment during cleaning than regular water? How to get rid of this residue?
Can you help?