Light brownish stains on liner


Jun 18, 2019
New York
Hi all, we have some light brown stains in numerous areas on the liner, at the bottom of the pool. Water chemistry is all good - I spiked the chlorine level high at the beginning of the season and cleared the water, water is nice and clear just have these stains now.

Is this due to metals or algae? Possible ways to remove and/or prevent this?

Thanks in advance!