magnum 350 made to bio filter only?

It would work but you would want to use media that doesn't compact such as Eheim Ehfisubstrat Pro, you would need to clean it out once in a while to get rid of any trapped waste but I don't think it will have to be very frequent.

Yes you can use a canister filter as a bio filter...

The Magnum may not be a good choice though as it has a small media container compared to other canisters...

I always thought the Magnum 350's biggest drawing point was it's mechanical filtration? I don't have one but would love to hear more from experience owners?

Wasting your time with a magnum-
The strong point and what made the magnum so popular is it's ability to be the best when it comes to mechanical filtration....

Just like the above response-It can be done with them-But the media area is alot smaller than what one could get with say a rena xp3.....

Overall the magnum should be strictly for mechanical filtration.....Period....

Fill the media container with ehfisubstrat or biomax and continue to use the blue magnum filter sleeves. This setup will filter a moderatly stocked 75 gallon aquarium. Make sure you rinse the filter sleeve regularly.