Do you think Emperor 280 filter will be too overwhelming for a 20 gallon tank? I have 3 very small goldfish in that tank.

I had the Emperor 280 for my bare-bottom 20 gallon tank (two black moores and a Japanese trapdoor snail) and it was awesome. You can either buy the pre-made filter cartridges or just stick the generic filter floss off a bulk roll into the media container for mechanical filtration. Do not allow the filter to suck up gravel, I think that's why mine stopped working. :angry:

Two of my 20s run with 280s. They works splendidly. A 280 has great biomedia space and reasonable gph for a 20.

I agree, that is the perfect gph for a 20 gal. tank. Your fish should be fine.