neon tetra disease

I had 7 neon Tetras for about a month. About a week ago one passed very suddenly. He was fine till an hour before and his only issue was swimming weird. Now another is sick and I can’t figure out what it is. It’s only swimming strange and it’s eyes seem bigger then the others, so maybe popeye...

Hello everyone, I'm a new aquarist. I don't have the readings of my water on hand, but my local aquarium shopkeeper told me everything is in tip top shape after taking a reading before I started adding fish. Two days ago I purchased 6 Neon Tetras and 1 Sewellia Lineolata. My question is in...