there are some ways i would have to disagree with this statement... most of the time, people consider quantity of the bacteria when coming to sumps... how much media can hold certain amount of bacteria, so we increase the filtration media and try to manipulate the water flow... but when using different kinds of sumps like moving bed filter, quality comes just as equal if not more... keeping strong bacteria culture on the moving media is the main obstacle. not to mention... people normally would overload media because they are afraid of losing fish. especially those who have expensive fish such as us fellow ray keepers. Stingrays are worse than goldfish in plecos in my opinion. i once underestimated the bioload of a stingray, and overestimated the efficiency of my filtration. amount of filter media per gallon of tank is no longer valid in the hobby. it really comes down to how much fish you have. im constantly improving my filtration by addingmore filters. infact im putting in a 4 foot biotower to my 180 gallon ray pup tank... it already has a fx6, 100 liters of k1 moving bed filter in a 55 gallon sump. i dont think sponge filters will do well in a ray tank..