Death of a fish, and i don't know why.

[classic-chassis]

I know it's not Arowana or CNF. Or any of the other monsters posted on here.
I keep beta or siamese fighting fish. I've got quite a few and i think they're tiny monsters because thery're preditors.
Anyway, I lost one today and i'm gutted, i woke up and knew something wasn't right with one of them because when i feed them blood worm they go mental.
This one didn't.
I look after them as instructed by breeders here, I even put parts of a leaf in the water which comes form a tree i have no idea of the name of, but it's natural medicine and gives the fish strong scales. (the arowana breeders recomend putting the same leaves in your sump fillter.)
Anyway, this morning this beta was not well so I jumped into action, Quickly changed the water just incase there amonia levels were too high,(i use water from a seperate tank that i fill outside the house so the chemicals go away naturaly). put in some fish med and some leaf parts.
The fish seemed like it was in pain, it kept going listless then sudenly swimming quickly. but upside down and bumping into things in its tank.
i kind of knew what the outcome would be, i didn't do anything with this fish that i did or didn't do with all the others i own.
It seemed a little bit swollen around it's gils and lower pectorial fins.
Any ideas what did it to him?

 

[ShadowBass]

No idea. Erratic swimming and swollen gills/pectoral fins could be several things. Infections of all sorts tend to cause those type of symptoms.
It would be really hard to figure out without seeing pictures or a really exact description, even then it may not be definitive.

Could it have just been old? Could the water have become contaminated in any way?

Most likely it wasn't anything you did since all your other bettas are fine. It could have been something you missed, or it could have been something that doesn't show symptoms until it's fatal, who knows.

Sorry about your loss. My favorite fish is a betta.
A lot of people here also keep bettas even though we have bigger fish too.

 

[classic-chassis]

^ I'm going to go against the advice of the locals and stop using natural products like leaves for medicine.
I think it was a posion of some kind and iIdid put a few leaf fragments in the tank a few days ago, that's why I did the fast water change when i knew it was ill, it wasn't an old fish and it was a stunner!
After it had died its spine was arched back, which would indecte poision.
I checked for bite marks becasue gekos go for them, but obviously I take precautions and there were no scares.
I am gutted because i take care of all my fish the best i can and there's always the niggling thought "is it my fault?"
I'd also like to add thanks man!