Inground gunite pool - stains on floor

Hi all-
First time poster. I own a 16 by 32 inground gunite pool. The pool is open and the water is perfect, however there are stubborn stains on the pool floor. I have tried clorine shock, and rubbing stains with a clorine tab, but they do not budge. I am prestty sure it is not algea.

Unfortunatelly, I did not cover the pool over the winter, however, there are not many trees around it, but this spring, there were some leaves and debri in it.

Any suggestions, it is a great pool, but the stains are ugly?

I will research the forum, I want to attach a picture, but do not know how.

Thanks
Murph

+ Post pictures using Picasa, Webshots, Flickr, etc.

+ Check your stains with a Vitamin C tablet -- if you leave a V-C tab on a stained area, and it clears or lightens -- it's metal. If it does not, its probably organic.