Levels from test strips are not very good, as they have too far a range to really know what is going on with the water. If you have a frog system, I think that uses copper - which can cause staining. With the levels you have, my suggestions would be to get your water tested by someone can test all your numbers without the strips. You can invest in a good test kit here on the Pool solutions web site, or you can get a decent kit at walmart for 13 dollars. You really need to get some chlorine in the water - and your ph is high, your alkalinity is high and your calcium (which you don't need in a vinyl liner) is high. I am surprised you don't have cloudy water. If the vitamin C tablet took the stain off, then it is metal - After you post the numbers I will see what is going on.