Review on Tetra Whisper Bio-Bag Filter Cartridges Small - 6 Filters (3 Packs with 2 Filters per Pack) by Stephanie Shatnawi

It's not really the particular filter's fault, but this whole type of filter (cartridge type) is practically useless. You should replace them at least once a week as there is very little filter media and by doing so you are removing all of the good bacteria needed for a healthy aquarium. I wish I had known this before I started this, it would have saved me a lot of trouble. I would not recommend this item no matter how small your aquarium is.