I sooo like talking shop about filters and stuff!
Here's a link to the media baskets for the 350 or the old 330's:
Click here and scroll to the last item on the pageAnyway, here's a link to bigalsonline and their 350's. To get a 350 for less than 30 bucks is quite the deal too!
Penguin 350This might be a little overboard but, theres a way that you can stretch the life of your filterpads for the penguin line of filters to 3-4 months. You only need a boxcutter and a steady hand. Cut out the little ribs on the backside of the plastic frame of the cartridge. Make sure you dont press hard enough to cut through the floss underneath. It might take an hour to do all six pads but once your done, its a breeze. It'll look like this when its done:
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Once your bio-wheels are getting nice and gunked up (and your media baskets are well colonized), you can spray the heck out of the cartridge floss (handheld showerhead on pulse or a hose sprayer, etc) from both sides and get 95% of the stuff that builds up. You should easily be able to stretch a 6 pack of filter cartridges into a year of use with this method.
I run two 330's on a 55 gallon and have never, ever had a spike due to cartridge cleaning with this method. I added it up and I'm saving something like 150 dollars a year!