Question:
Where we live at a condo complex there have been issues with algae in the pools and or spas. I reported it and one of the excuses I got from the health department was that the automatic fill openings locate by the spa and pool are made of black piping which may look like black algae. I just don’t understand or see how piping can appear to look like algae when the pipes are pipes and not something that is going to blend in with anything? Originally they indicated that it has the black and green build up and would have the pool company clean it. But then today they tell me something else?
You may have some scaling, and calcium deposits, and that may get some black tinting on it from organic materials and deposits, or metal deposits if metal leeches out of metal pipes and/or equipment.
The lid of your skimmer and skimmer ring look like it could be a bit of both.
I’d ask to have a scale reducer added to the pool, and treat with a shock to get it up to 10ppm (no swimmers while the level is spiked like that) and it should help clear up issues you may have.
I am not aware of poly/black pipe causing black issues in pools. We have many pools that have also used black poly pipes, haven’t experienced anything similar.