A friend of mine bought a house with an old pool, not a horrible shape, plaster needs to be redone soon and needed a new filter, chlorinator, but otherwise decent. We finally got pretty much everything under control, his chemistry is good, but then he decided to get algaecide and just about next day the dark spots on the bottom of the pool are back again (there were there initially, but almost completely gone away after the chemistry was stabilized.)
So, im thinking the stains are related to algaecide, but I'm certainly no expert...
I'm not sure exactly what all his numbers are right now, but he will test tomorrow and I will post them up once I have them, but the last time I tested, everything was within range, though CYA was a bit on higher side at 60ppm.
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