Due to the unreliability of the local pet shop to have any feeders in stock, I have purchased a 20 gallon tank to keep a bunch on hand. It is a 20 gallon tank and the filter says it is good for up to a 40 gallon tank. How many medium sized comets could I keep in there? How about goldfish? I just cant seem to find any 2 sources that agree on this subject. Thanks.