Hi, I added a small goldfish last night and a snail, both from Petco. Today, my three bigger fish (3 inch long) are all gasping for air alot, T THE SURFACE! THAT'S NEVER HAPPENED BEFORE. aLSO, one has a red mark on his side. I attach a picture. Not sure if it was an isolated incident with him, or if it's an illness that the other 3 fish are also getting. I also changed the filter, one of the little whisper filter for 10gallons, not a fancy filter, just regular filter. I have a 90 gllon tank I am waiting for the wooden stand to be built and then I am changing these fish into that tank. To help with ammonia issues. Thanks, I typed this very fast because I'm very worried. Starting a 30% water change literally in 5 seconds. THanks!