Yup leave your cleaning of the XP3's at 6 or 4 month intervals. like a force of entropy proteins will start adhering to your media and foam. Thing is these proteins starts attracting more particulates which then adhere to the brown gunk coating. This takes time, every time you overly clean your media it releases the proteins from being binded to surfaces and means that particulates will slide past and back into the tank.
eheim webpage explains it thus:
On the surface of the filter medium protein particles (size 0.001 - 0.00001 mm) change their electro-chemical properties. They lose their solubility and settle on the surface of the filter medium. Further protein particles follow, covering the filter medium with a protein layer.
This protein coating is highly adhesive and retains even fine particles. This explains why the filtration performance of new or freshly cleaned filters is not satisfactory. The adhesion does not become effective until after a few days, when sufficient protein has settled. If attempts at combating turbidity by cleaning the filter are made too soon the adhesive coating is destroyed and the aquarium remains turbid
Turbid means visible particulates in the water.
eheim webpage explains it thus:
On the surface of the filter medium protein particles (size 0.001 - 0.00001 mm) change their electro-chemical properties. They lose their solubility and settle on the surface of the filter medium. Further protein particles follow, covering the filter medium with a protein layer.
This protein coating is highly adhesive and retains even fine particles. This explains why the filtration performance of new or freshly cleaned filters is not satisfactory. The adhesion does not become effective until after a few days, when sufficient protein has settled. If attempts at combating turbidity by cleaning the filter are made too soon the adhesive coating is destroyed and the aquarium remains turbid
Turbid means visible particulates in the water.