Male Betta Died

[paudie22]

i was looking at my brothers tank yesterday and i noticed his male betta had a whitish mark on each side of his body as if he was turning white (he was red). i checked the water stats and everything ok, i changed roughyl 2 gallons of water and treated with melafix until i could get to the lfs today. but when i woke this morning he had died. he was in a 15 gallon tank with 2 shrimp 2 otos 2 mollies 3 guppies and 2 platy. what could cause him to go so quickly and would it be infectious

 

[LauraFrog]

How long has the tank been set up and how often are water changes done? Water stats (ammonia/nitrite/nitrate) would really help.

Where is the white? If it's at the top of the body on either side of the dorsal fin - it would possibly be in front of the dorsal on a betta - this sounds like a 'saddleback' lesion. This is often caused by columnaris. Did you notice anything around his mouth?
If it was columnaris, this is a bacteria that usually inhabits the slime coat of fish. It's present in most tanks and virtually impossible to eradicate, but it doesn't often cause problems.

If he died because of columnaris and the other fish arent dead, it's probably because he was weakened by stress. I'd suggest that would be caused by being in a community tank. Some bettas thrive in this kind of environment but others just don't have the temperament for it and much prefer to be alone.