I have two Marine 1 clear cannisters with carbon in them and algae
growing in them. It is a very good secondary filter system. Some large
Public Aquarums cultivate algae filters with artificial sun lamps. The
trick is the UV still keeps the water clear. Bio filters are best kept
in the dark. The algae and carbon filter is for water purification. To
much Rain will also cause the greenies the PH starts to dip and the
water looses hardness. If that happens add some lime chips in a
pantyhose to the water flowing in and that should help. Or if your water
is hard do a slooooow water change 10% every few days. Keep smiling AL