This tank has been a challenge. I have been battling what I think were dinos. Everytime things seemed to be going in the right direction, within days it would revert back to something nasty looking. In the end I think it was the rubble rock I put in there (in the pic above) then dumping sand on top of that. I removed the rubble and some of the coarser sand along with a couple of the frag racks. Within days the brown, nasty, stringy stuff was gone. Whatever did it, I'm happy that it seems to be on the right path.
Here's how it looked today.