betta swims erratically around sick

Question
5 gallon tank one betta three heterandria formosa setup three months. Betta acted and looked healthy. greeted me, ate fine. showed him mirror like other times. He flared at it. Suddenly he swam wildly around the tank. Like he was having a fit. Settled down. Then hed swim to one spot stay a short while then move fast to another stay there then move again. Put light on him Saw gold coloring by gills. A very fine dusting on body. Can only see these things when light on him. Never scratched looked otherwise healthy. Soon he satyed at his favorite spot. Gills moving slowly and wide. B arely responded to stimuli. Enede his suffering. What could happen so suddenly and kill in less than a day.

Answer
Hi;

It sounds like he had a case of velvet. It is a tiny parasite and can be very itchy so he was exhausted from trying to relieve himself of the nasty little bugs. Here is a link to a page about diseases bettas are susceptible to, just scroll down to the "velvet" section;

http://www.bettatalk.com/betta_diseases.htm

Velvet is VERY contagious so you should treat the others if it turns out to be what your betta had.

At Your Service;
Chris Robbins