in the last 2 months ive had 1 of my guppies die and my Cory Catfish..Anyhow its the manner of which They died.. It looks like he had as A$$ kicked solid till he died.. Ill begin my story. The first Fish was around 2 months ago... I found my cory Cat with a what looked like bloody fins and just a savage beating.. he was dead when i found him. So i took him out checked my params and Ammonia was close to 0 I say close because it wasnt the exact color of 0 Nitrite was the same half 0 color? and Nitrates where 20 area.
Now the next question for people to ask is what mean fish do i have in my tank. My tank is guppies,Neon tetra, Kuhli loaches, Mystery snails, Ghost shrimp and 1 male 1 female betta. Now before we go into the bettas being the killers here. I removed the Female the day the cat died as i assumed it was her. AS she is the newest fish. the Male Betta has been in the tank for 2+ years. Also I dont believe either the male or female are fast enough to Attack and Kill the Cory Or Guppie. I was actually thinking that when the Cory Cat died the other fish where eating him.. well the other day i found a guppie in the middle of dieing he also had his butt kicked... female betta is still out of tank for the moment. i have no clue what this is.

btw the tank is a 65g tall so 36 long 25 tall and 18 Deep. i forgot to add that..

i did a little research, and i'm by no means a fish expert, but it said that those loaches like to be in groups of 5 or more, is it possible that you don't have enough so he is stressed and uncomfortable and therefore aggressive?

those seem like the only fish able to dish out such a beating

even though those tetras can be pretty viscous sometimes XD

otherwise, as unlikely as it may seem, it could just be the betta

I actually have 5 of those loaches. I know its possable its the betta but he has been in the same tank with the same fishes.. if i get another death ill remove him and see.. really the neon tetra's? i would of never guessed them.ill have to keep a close eye on them. thanks!

Sounds like the Betta to me. Guppy is easy to see, especially if it had a fancy tail.

Yeah I have difficulty believing it wasn't the beta. It is the most aggressive fish (just based on the nature of male betas) in the tank. And like you mentioned you have a group of loaches.

__________________

Remember you said this happened shortly after you added the female betta. He may have been fine before there was a woman involved, but then you drop in the girl and suddenly he's all, "RAR! Look how tough and what a bad boy I am! Doesn't that turn your crank, young, attractive, only female in my world?" And then the female ups and leaves and so he's even more cranky, taking it out on the other fish. Like, "why'd she leave, eh? Did she tell you why she left? Answer me!!!"

Sometimes I find it's hard to understand bettas unless you think of them as being 1950s Greasers.