The stringy stuff ... is it coming from the anus ? If so, this means internal parasites and they need treated food, or Maracyn-Two in the water. BUT, don't do this in the DT
Get a QT tank running
The powdery-looking stuff ... could be brook
Look up brooklynella on the web and compare pics. This stuff kills clowns and you should do some research on how to cure it, and fast as it's a quick killer