I recently went to one of the fish stores in the area and in almost all their tanks they have undergravel filters installed. The owner told me that for tanks 30 gallon and under a undergravel filter was all you needed. While I was growning up I had a undergravel filter in my 30 gallon but back in the mid 70's I'm not sure if they had the other filters or not, all I remember is that they had those rectangular clear plastic filters that you put in charcoal and cotton into it and then use a small pump and airhose, boy that was along time ago. SO is it true that undergravel filters are the best for 30 gallon and below, or would a combo of both filters be better???