Identify pool stain and ways to remove

[yuyiwen]

I am first time pool owner. There were lot of leaves at the bottom of the pool when I bought the house, the water is clear. I vacuumed and brushed the pool multiple times but could not remove those stains. They are dark (black) in color. Can anyone help to identify the type of the stain and suggest ways to remove it? Thanks.

 

[JasonLion]

The first step is to narrow down what kind of stains those are. They look kind of like iron stains to me, but they could be organic stains and it is also remotely possible that they are calcium scaling though that seems unlikely. I suggest starting out by putting a vitamin C tablet on one of the stained areas and seeing what happens. If they are indeed iron stains, the vitamin C will remove the stain in the immediate area where the tablet was. If they are something else the vitamin C will not have any effect and we can try something else.

 

[yuyiwen]

I will try the V-C tab method this evening. I have some V-C tab at home, but they are not chewables, can I use those? A single pill tends to move at the bottom of the pool even without pump running. What's the best way to stop the movement?

By the way the pool water's CH value is approaching 1000. I will be replacing more than half of water very soon.