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underwater filters


May 8, 2003
Are you refering to the undergravel filters, if so, they aren't recommended. The Octo usually disturbs the filter, or might feel adeventurous, and make it's way down one of the uptakes. Octo's tend to disturb anything in the tank.

Hope this helps.

Jan 21, 2006
No, this isn't an undergravel filter. It goes in the water and does not hang from the tank. I believe it is the Fluval 4 Underwater Filter.

Thank You
Jan 4, 2006
I have a Fluval 404 on my Bichir tank. It is commonly called a "canister filter". You have a 1 inch tube that goes in and out of the tank. This makes it easy to make ceph proof. It works well once I get it primed. I can just let it run and run and run.

The only problem is the protein skimmer that you will also need. You will need a hang on the back type, whcih presents its own problems. But the filter should work fine.
Jul 18, 2005
Hi SM,

First, just to be sure that we're all singing out of the same hymnal,
here's a link to a description of the Fluval 4:

Assuming that you're following the recommendations about tank size
(50+ gallon) for a bimac it would appear that you'll need at least two
of these to provide sufficient filtration. Keep in mind that an
octopus is a messy eater with a high metabolism and a big appetite.
The consensus seems to be that you need two to three times the
filtration capacity for an octopus than you would need for an
equivalent amount of fish. The Fluval 4, which seems to be the largest
of this type of filter available, is rated for a 57 gallon tank which
means that two of them might be enough but one definitely wouldn't be.

One other minor point. The pictures that I can find don't show
sufficient detail to tell much about the intake screen. Octos have a
reputation for injuring themselves on pump impellers so you might need
to install some sort of auxiliary screen to keep curious arms out of
harms way. Then again, the existing screen might be OK as is.

You might want to do a Google newsgroups search on "Fluval 4". I just
took a look and there seems to have been quite a lot of activity (530
hits) about this filter so you ought to be able to learn something
about its effectiveness and reliability.

Submersively yours,



TONMO Supporter
Mar 15, 2003
Good points, all. I've never been a huge Fluval fan, but some of the other members here are...but, as stated above, you are going to run into some issues with any "hang on the back" filtration.