Clear to white stringy poop can also be a sign of internal parasites. You can get a medicated flake food from most independent / good fish stores and online (like Peabody's Paradise http://www.peabodysparadise.com/ )usually have some. I have used, and will use with new fish - one with praziquantel which is where mine came from. Follow the directions. There are different kinds of medicated flakes. See which might work best for your problem.