Just opened up our pool after Winter. This is our 4th year of owing a pool and usually on opening there is some algae and general detrius. This year the whole bottom of the pool is covered in one continuous sheet of dark brown substance. On removing the winter pool cover it looked a bit like an alien landscape as some of it was pulling away from the bottom and floating up in small sheets. We've removed most of it quite easily with a brush and net. It comes away in long strips and as it is removed a lot of bubbles escape from under it. The substance keeps it's form when held and is slimy, bit like the feel of seaweed. Tried looking it up, but can find nothing on it. None of the pictures of algae look anything like it. We are disposing of it but I am curious to what it is and if it can be composted or not. Thank you for any help