I live just outside of Baltimore, MD. Last summer we had a bit of yellow staining that seemed to disappear when I applied a Vitamin C tablet to it. We opened the pool early this year, in April, to deal with the staining. We bought Stain free, applied it twice, and the stains didn't go away. We shocked the pool, it, did not get better.
When we opened the pool there was a new stain on a step in the shallow end.
Our pool company came out and said it looked like a leaf or something natural/biological. However, to us, it seemed to almost be coming from inside the plaster.
As as for the yellow staining he said things like discoloration motling, discoloration of plaster. He also said we need to remove scale and to look for products called Scaling Connie, Dr. 40, hydro quest and scale free. We didn't do any of that because we thought maybe we would redo the plaster instead and he said some of these products are difficult to find.
In/around June we had green algae growing all over. We took in samples a few times and we couldn't keep our chlorine level up. We treated our 35,000 gallon concrete pool with fifty five pounds of chlorine. It killed all of the algae.
We took samples in throughout the summer and our numbers were good. On occasion our chlorine was low but it never required more than a small bag or two.
Now, over the last few weeks we have a spider web type yellow stain around the pool (see photos). It does not come up with brushing. We took a water sample in today and were told we again have zero chlorine.
The pool is 10 years old. We have never had a problem maintaining chlorine until this summer. The pool is mineral/salt.
if anyone has any idea what's going on, please help. We had another company come out last week who said it could be mustard algae however we are not in the typical geographic region for mustard algae and it does not disperse when we sweep it.
Thank you again and again!!!!