Dark stains on vinyl liner

[nisqu]

I still need some help. i just ordered the test kit, but using what I have I get the following: TC 10 FC 10 PH 6.5 ALK 40 CYA 0-10.
I added 5 lbs CYA about 3 weeks ago and my reading did not budge.
I shocked last night so the chlorine #s are not usual. My stains are not metallic. they respond to shock, but do not respond to the brush. I did not have them last year. I need to know how many PPM of bleach I need to get to for a strong shock. I have 6% Ultra from WALMART, but I need to know how much to use.
Any help is appreciated.

Nick

[buckeyemom]

We had this last year, with the same results, that it responded to shocking and then came back. But this year I switched to the BBB method, and our pool water looks like liquid glass, and no stains!