Pool liner stained

Hi all, I have a big stain problem (caused by a previous guest) that I've not seen in 8 years of having the pool. You can see from the picture a green/yellow above the water line. I can only assume this has been caused by suntan lotion of some sort of false tanning product. There are one or two drops of the same colour on the pool floor so can only assume they were applying suntan lotion in the pool and some got spilt.

I've tried all I can think of to remove the stain, but its not shifting...

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