Thank you for responding Simmons99. I have not tried to rub a vitamin C tablet against the stain, I will try that. As for the CYA number, I do not have a tester for it. I bought the test kit from Leslies and that is not one of the tests. Are ther individual test kits just for CYA? If not should I bring my pool water into the pool store to test?

Thanks again.