Bests & Worsts Reviews from Amazon

Too much bypass, i.e. too much water flowing through the sides of the filter compartments. Water is supposed to flow first, through the most bottom filter compartment, then through the compartment on top of that. However, due to the bypass issue, water flows through all the compartments at will. As a result, my top biological filter compartment began to fill with gunk, which is supposed to be removed by the bottom three filter compartments. I finally managed to fix the problem by wrapping a 6 mm expanded polypropylene (EPP) sheet as shown in the picture.