I don't know what kind of "liquid shocker" you gave him, but even if it's plain 6% bleach (which is what I strongly recommend he use), 5 gallons in a pool that size should raise the Cl to above 20 ppm--and if he had already added chlorine in some other form, the Cl level would be possibly high enough to bleach his liner. It would be a much better idea to know the CYA reading, as Carl said, and then calculate how much chlorine to add rather than just guessing at it.
Janet
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