SurfSteve, feeding Cat Chow is likely to have a high amount of waste in the form of undigested material.
if your fish are above 6"long feeding would be 1.5-4 pounds of feed per day fed over 2-4 periods per day. This would be the rate if using Purina Aquamax---a highly digestable food for fish.
An educated guess for using Cat Chow would be to feed 3-10 pounds Cat chow and get more filtration to handle the high ammonia load.
Compare most dog feed daily feeding rates for a 100# dog. Common brands will suggest 10-15 cups feed per day and will produce lots to clean up at the other end of the dog where Purina Pro Plan, a highly digestable feed requires 3.5-4 cups daily and produces little waste daily at the other end. The good feed may cost more, but overall expense is lower along with cleanup cost. Not to mention you'll have a healthier, less stressed animal.
