I, PERSONALLY, AM NOT CLEAR AS TO WHAT 'STAIN' YOU'RE REFERRING TO. ARE YOU REFERING TO AGEA? MOLD/MILDEW? IRON STAINS? OR WHAT?
I DID FIND ONE THING ON THE WEB. PERHAPS THIS IS WHAT YOU'RE REFERRING TO???
Diamond Brite Stain?
Q. I had 'Classic' Diamond Brite put in my pool and there's a three foot dark spot at the bottom of the steps in the shallow end and around the main drain. The contractor wants to drain the pool and acid wash the dark areas. Will this stain be permanent?
A. Diamond Brite is finished with an acid wash which takes the 'haze' off the surface. I'll bet the 'darker spot' is actually where the Diamond Brite is fully visible while the lighter areas still sport the haze. Have the contractor drain the pool but ask him to first try lightly acid washing the lighter areas of the surface.
IF THIS DOESN'T HELP, THEN YOU NEED TO TALK TO A FEW POOL INSTALLERS UNTIL YOU GET A STRAIGHT/CONSISTANT ANSWER.