sounds like cotton mouth...but a pic would really help id the issue.
Here's the syntoms/treatment and prevention...hope this help.
Symptoms:
White spots on mouth, edges of scales, and fins
Cottony growth that eats away at the mouth
Fins disintegrate beginning at the edges
'Saddleback' lesion near the dorsal fin
Fungus often invades the affected skin
Rapid gilling in cases where gills are infected
Treatment:
Change water
Vacuum gravel
Add aquarium salt
Treat with copper sulfate or antibiotic
Discontinue carbon filtration during treatment
Prevention:
Quarantine new fish for two weeks
Maintain high water quality
Provide fish with a nutritionally balanced diet
Medicate fish prophylactically before moving them
Disinfect nets and other equipment before using
This I got from
http://freshaquarium.about.com/cs/disease/p/columnaris.htm.
But copper sulfate works IMO.