Hi, Live in the Algarve, Portugal, I have a liner pool which has clear water but the liner has gone a dirty brown colour. Last time this happened I added acid although the water balance was good and in a few days it cleared and came back to blue. This time nothing works.
After rain the water went slightly acidic so bought the ph and TA back to normal but gradually the liner goes patchy green/brown on bottom and sides. Will not come off with a brush. Definitely not algae.
Strange thing is, if a worm or snail etc gets in, where they lay goes back to blue/white as if it bleaches the stain. Also when the water level drops the newly exposed to the air liner goes from brown to white/blue.
Pool temp now 13 degs C, and pool size 10x 5 metres 2.5 metres at deepest. Pool water is always mains water, not borehole. Pool liner is getting old around 11 years.
Anybody have any bright suggestions please?