Magnum 350 Simple Modifications

Written by Kmuda. Posted in All About Equipment

The Marineland Magnum 350 does not have a good reputation with many aquarists. Not because it is a poorly manufactured filter, it is a well made product (I have one that has been in constant use for 20 years), but because it is not flexible. Since the Magnum 350 is designed primarily for Carbon filtration, without a Bio-Wheel attachment there is no mechanism for bio-filtration.


This easily resolved by simple modifications.


First, get a reverse flow kit for a Penguin powerhead and attach the strainer/foam pre-filter from the kit to the inflow tube of the Magnum.

Next, take the media container and toss the carbon. Fill the media container with a biomeida. My preference would be Eheim Ehflilav because its size is perfect for the Magnum media container and it retains its biofiltration properties even when there is a shortage of mechanical filtration. Since whatever media is in this cartridge will become gunked, Ehfilav is a perfect option. However, I have used everything from Biomax rings, to Matrix, to Eheim Ehfisubstrate Pro.


The powerhead strainer and sponge serves as mechanical filtration preventing the bio-media in the container from getting clogged. In addition, it greatly reduces maintenance requirements as it performs a majority of the mechanical filtration and is easily cleaned during water changes.


With the prefilter in use you have the equivalent of two trays of mechanical filtration (the powerhead sponge prefilter and the filter pad surrounding the media container). Include the media container and you now have the equivalent to a three-tray canister.


Finally, it is best is to add a Penguin Bio-Wheel Pro 30 or 60. Nothing beats a bio-wheel for bio-filtration. Adding the Bio-wheel, in the suggested design, may actually result in the Magnum outperforming many more costly filters. Adding a Bio-Wheel 30 results in the equivilant of a 4 tray canister, and the Bio-wheel 60 a 5 tray canister.


By doing these simple things you have turned the Magnum into a very effective filter.


Links to the components I mentioned to improve the Magnum are listed below:


  • Ehfilav - You can get about 1 box into the media container
  • BioMax - You can get about 1 box into the media container:
  • Ehfisubstrat Pro - Smaller than BioMax so should work better in the Magnum Media container


Note: I do not have a link to the Bio-Wheel Pro series. I purchased mine with a Penguin Powerhead. Incidentally, the powerhead came with the reverse flow filter kit.


Note: Everything mentioned above also applies to the Marineland HOT 250.