I use a whisper on my goldie tank and have never had a problem with the intake being to strong for them. Is the tank crowded? Do the fish exhibit any other signs of illness (usually this is the only reason fish get sucked into an intake, they are too weak to fight against the current).
I guess if the fish are just getting fed to something, an injured tail isn't all that important....but you might want to make sure there isn't any illness in the tank, i'd imagine feeding sick fish probably isn't a great idea.
its not supossed too have a sponge there but you can put one on it and it wont effect its filtering by much at all, i had a sponge on my power heads so my anemone wouldnt get its tenticles chopped up and it worked just fine, you might also want too try putting a piece of nylon on the intake and hold it in place with an elestic, that is what i do when ever i have fry in any tanks
Your feeders are ill. Are these feeders you are buying from the lfs? If so they are often ill due to stress ands overcrowding. That is the smallest filter they have and it really isn't powerful enough to suck up a goldie unless its already sick and weak.
God, let me be a light and let my life show someone your awesome power.
davoz is right there most likely in poor heath from your lfs, you should try rosy red minnows there a bite healther but the safest and healthist would be feeding ghost shrimp instead of gold fish gold fish are messy and full of fat