My pool has been perfect all year. I went away a month ago and only had someone to bleach the pool a few times, so i bought some HTH algeacide, and the HTH chlorinating tablets. Ever since i've used the algeacide and tablets i've had these black spots on the pool floor. I thought it was algea for a while so was shocking the pool, but they just wouldn't go away. I would vacuum to waste and they would come right back. then one day, while i was vacuuming, i felt the spot and it felt like dirt, very grainy. So I thought it couldn't be algea. I did some reading here and thought mabye I had metals(copper) in the pool. I took the water to the pool store..no I don't have a test kit that tests for metals...and 2 places told me no metals. One place told me that is was probably from the HTH chlorinating tablets if they contained calicum hypochlorite. I checked and they don't, they are trichlor. The algeacide isn't polyquat though...I know i'll never do that again...so not sure if that caused the problem. The guy at the pool store told me to stop using the tabs...thinking they were calcium hypochlorite..and vacuum to waste several time a day, and eventually the spots would go away. I tried that today, and already the spots are coming back. Im getting frustrated and would like to solve this before I close the pool in a few weeks.
So, now after all of my rambling what do you think?
Here are my numbers