I am currently using an Aqua-Tech 10-20 HOB Filter for my 20 Gallon tank. Currently I have it setup so there is sponge, then the filter cartridge, and finally the biogrid. There seems to be an excess amount of bypass. Is there a better way I can set up the filter for optimum filtration and flow? If I have to drastically change the setup, how do I keep the beneficial bacteria?