My hoses on my mag. 350 cannister filter have started turning a yellow /brown inside, almost like an algea, but both hoses are shielded from all light, is this normal ?? the tank is in it's 4th week of cycling and the peak was last week so another couple of weeks i guess, and maybe another water change and a rinse [ in the water from the aquarium] what is causing this discolorzation in the hoses ????