The used tank that I bought, 4'x12"x18", came with a Marineland Emperor Model 400B bio-filter. It has the two blue carbon filled filters, but right next to them, is two grey hard 'boxes' (about 1-1/2" wide) that have white stones and cylinder shaped black charcoal in them. Is this a double filter system? Oh yeah, there's also the two bio wheels that are like new. Is it okay to continue to use the stuff that's in these boxes? Is it necessary to use this boxes at all? Can I still use the two blue filters, as they still look like new. :help:
Last edited: