I currently have one telescope eye goldfish in a 10 gallon tank. Today, I found that my second goldfish had died(RIP TweEk<3). Now, when I bought the fish, the fish man at the pet store told me that a 10 gallon tank, for two goldfish, without a filter, would be fine as long as I took care of it. At this point, I realize that the above is incorrect, and just bought a filter for the tank. I purchased a Tetra Whisper Internal Power Filter for 2-10 gallon aquariums. When I got home, and began setting the filter up, Pinto, my last fish, was fine. Very soon after, she began sitting at the surface, gulping at air. That was an hour ago, and she's still doing it. Why the fluff is she doing this?