I have a 28' round AGP. I did not use a cover during the winter. There was a pile of leaves in one spot where the current of the water piled them up. I cleaned those out & my liner looks brand new in that spot. Every where else looks real dull or almost stained. The patter of the discoloration or stain of the liner is sporadic. I've tried brushing but it doesn't help. Is this something that will go away when the chemicals are balanced?