I'm now at a loss. I had the water tested to find all was in order (some low ALK), but 0.4 ppm iron (no copper). They gave me a bottle of Metal Away, or whatever it is called (yes, yes, I know...) and it did nothing I can see. They also threw in a couple of the sock bags and said to run it for a couple of days, backwash, repeat.

Although the backwash did show a healthy amount of brown, the water remains green-tinted and hazy in the deep end (clear but tinted in shallow).

All I have left to try is to add some DE to the sand filter, and also hunt for a proper chelation agent.

Any other thoughts?