Bionood ceramic cylinders are supplied with both Aqua One's Aquarium Series and their excellent Aquis and Advance Canister Filters because they offer such excellent biological filtration capacity. Change a few regularly to maintain an efficient and stable bacterial population.
The Clear Cover is the transparent plastic section which shields the lighting tubes in the canopy from water splashes and spray etc. These frequently become scratched and scuffed over time reducing the amount of light which penetrates the water’s surface. You will be amazed how much difference a new one can make.