A lot more info is needed. By air filter are you referring to a filter that works using a air pump like a box filter that goes inside you tank? A filter like this does not adversely affect plants. I use them in a lot of my planted breeding and grow out tanks.
What size it the tank? What kind and how much light. What kinds of fish other than gold fish? How many fish? What kinds of plants. What are you water parameters, PH, nitrites, nitrates, hardness? Sounds like you have something going on other than a filter issue.
Atlanta Area Aquarium Association
North American Discus Association - Vice President