We have a metal frame with vinyl liner 12'x3' (approx 2900 gal) above ground seasonal pool that we bought brand new in June, after struggling with cloudy water almost immediately (even with proper chlorine levels, shocking weekly, and algaecide) we finally lost the battle with our pool and decided to just drain it clean it and start again this past weekend. Before we drained it I was going through 3 - 1" chlorine tablets a day with a pretty stable 3-4ppm chlorine level and I had noticed a build up of this black tar like substance in the skimmer and when we drained the pool I cleaned it with bleach and that seemed to get rid of it fairly easy.
When we refilled the pool on Sunday we decided to switch from chlorine tablets to LC and I added about 16oz in the evening along with some algaecide just as a precaution, the next morning around 9am I checked the levels and it said it was at 6ppm. I checked again at 2pm and it registered 0ppm..... we live in the central valley of California where it's triple digits usually June-Sept and there is a ton of organic matter floating about in the air because of all the agriculture. I've continued to put 15oz of chlorine into the pool every evening around 8-9pm and testing every morning around 9am and getting the same chlorine level of around 6ppm - but usually by 11am the chlorine level has dropped to 0ppm. Does this seem like excessive chlorine usage or is it normal for 100+ weather and sunny days? As long as the chlorine level is high overnight will it do it's job sanitizing the water safely?
Today I opened the skimmer to clean the filter after letting it run nonstop since Sunday and found the black tar there again! No one has been swimming in the pool since we refilled it so I don't think it's an oil build up. Could the excessive chlorine usage and the presence of this point to black algae or some other fungus? Or could the black tar stuff actually be from the algaecide itself?
Here's a photo of the gunk in question, aside from this the water is crystal clear and looks great! I'm just worried it won't last if I can't stabilize the chlorine level.....