thank you for the input. i currently have an undergravel filter and a cascade 300 on my 55 and im planning to move the cascade to a 55 by itself and put the bio pro system on the tank with the undergravel filter. (it is my showcase tank upstairs that all my visitors see) currently stocked with 7 convicts 1-4", 1 venz pike 5", 2 green terrors 3 & 4", 1 firemouth 4", 1 blood parrot 2", and last but far from least (bio-load wise) 1 pleco 12". so i want to have a very well operating filter on it to make sure my water stays crystal clear and has no ammonia with a high bio-load.