dead betta

[KnightFire]

This afternoon I got home from work to find my betta had died. I have had him 3 months and on sunday I bought a ghost shrimp to go in his tank and help keep it clean. He didnt get on very well with it (lots of flaring and chasing) but if it stayed out of his sight they seemed ok.
This afternoon he was just floating in the tank not moving, and the area around his mouth seemed to be a little white and kind of crusty.

I havent checked the water params yet (just got in) but on saturday they were fine (ammonia 0, nitrite <0.3, nitrate 12, pH 8, GH 9)

Any ideas to as to a possible cause?

KF

 

[KnightFire]

Tank parameters are all fine.
pH 8, GH 8, KH 7, Ammonia 0, Nitrite 0, Nitrate 12

There is a kuhli loach living in the tank too at the moment, but he never had any problems with it so I doubt i was a fight, he didnt seem damaged in anyway other than the flaking around his mouth.

KF