I need help. I have tetra second nature whisper hob filter for my 55 gallon tank. I do not hink the bio foam that sits in front of the bio bag is enough for bacteria growth. I was thinking of rigging it with seachem matrix in place of the bio foam. The question is I have 2 separate bio foam pieces since its the bigger filter. Should I replace just one at a time? My fear is that I will lose any aerobic bacteria that is on this flimsy piece of foam. any suggestions? I was also going to start using the PURA FILTER PADS YOU CAN CUT TO SIZE RATHER THAN THE BIO BAGS that don"t seem to trap small stuff. I know everyone says just use poly fiber ,but I don:t think they drap small debis.