Everything has been doing great for about a year now, but today I lost my first fish in for over half a year. It was a little 2 inch rainbow fish I'd been taking car of since it's infancy. There are 2 other 3" rainbow fish that stay at the top of the tank sucking air like they can't get enough oxygen. All the other fish are behaving normally. I use nothing except pure water purchased at my local aquarium store. The weird thing is even after a 50% water change they were back to doing it within 24 hours. I have a canister filter with a UV filter. Since it's summer and the tank is by a window I turned the heater down a little b/c sometimes hot fish will stay at the surface. The only thing that's changed is I introduced 4 of these African dwarf frogs, purely aquatic and not more than 1.5" and a couple new plants, everything bought from a local aquarium store. I'm also using a new brand of frozen brine shrimp for the last 2 months without any issues. So yeah I'm out of ideas. If the fish community has any ideas it would be most welcome.