The smaller of my two bubble-eye goldfish is always getting his bubbles stuck in the filter tube... I don't want to reduce the effectiveness of the filter by covering the tube. Any tips?
Just cover the tube. You should have your fish in a 40-50 gallon tank if they are the only fish in the tank. You should have a filter that is made for gallons 65 gallons and up, as Goldfish are very, very messy fish.
Just cover the filter with a nylon stocking, it won't reduce the effectiveness, it will just stop him from getting sucked into the filter. If not a nylon stocking, just get a thin, aquarium sponge found in pet stores.