There is a large and effective foam pre filter. If your worried you could put a pad in the bottom tray they tend to clog very quickly but in my experience that just means the filter is doing its job. It ultimately comes down to how often you can maintain it (Open it up and change out fine filter pads) If you go too long with the fine pads flow starts to really decrease.Dempseygunz;3101401; said:If I just use bio, isnt that going to allow some particles to flow through?