I have a 10 gallon planted tank with a betta and what used to be 5 peppered cories. There are a couple MTS, ramshorns and assassin snails in the tank too. The remaining three cories seem to be happy and healthy, but the other two just died out of nowhere. I'm getting a bit concerned, and I really don't want the other three to die off too.
I did a water test with the master test kit that I recently picked up, and everything was fine. My tank is fully cycled, and the nitrates weren't very high.
The first cory to die passed about a week after I introduced him to the tank. This was several months ago, back around Christmas. Now just the other day, a second passed. Both were floating at the top of the tank, with their bellies up. I noticed that both cories at the time were the smallest in the group... Could this have something to do with it? If so, how can I prevent this from happening again?
I feed the cories two Omega One veggie discs every day, one with each feeding I give my betta. The temperature in the tank is 80 degrees F, and the tank gets approximately 10 hours of light each day. All of the plants are happy and healthy and growing like weeds, and my betta appears to be okay. He's very social and likes to swim with the cories along the bottom of the tank. I've only ever seen him flare and chase them a couple times, and it's always only for a short while. He's never actually hurt them before, so I know my betta isn't to blame. What could it be?