Hi folks I'm new to the forum and am having just major problems with staining in my Splash Superpool (vinyl) - it's 8,000 gal. 13 x 21 ft. purchased in May 2001. It started as a very small area of dark dark blotches and streaks, season before last, the folks I purchased the pool from came out and put in 4-5 lbs shock, seemed to clear it up temporarily, but last year is was worse and this year it is horrid, I'm just sick! It is getting all over the walls and in the floor too. I have spent a fortune trying everything under the sun for metals, scaling, algae and metal trap filter for refill water. Finally got another company to come out and take a look at it Friday. They said it was blue-green, black algae and said Polyquat 60 WOULD get it. So yesterday morning I picked up the Polyquat 60, put in the recommended dosage after lunch and waited for my miracle, so far this morning (8 am) - NOTHING - I just want to cry. You can scrape this stuff off with your fingernail, but it will come back in a few days. Has anyone heard of 'clorine stains' - is there such a thing? I'm open for suggestions and desperately need help - It was such a beautiful - easy to care for pool for years. Thanks everybody.