How do you clean dirt stain line at bottom of gunite pool due to faulty pool sweep?

I seriously doubt that the pool sweep is the problem here with your stains. You will have to describe the stains in order to get to the root of the problem.

Are the stains:

Rust color or brown?

Black or gray?

Green?

Blue?

Are the stains consistent or uniform? Are they all over the pool? Do they cover the whole pool or are they in small patches?

Answer these questions and I may be able to tell you the cause. k