06-05-2010, 10:39 AM
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The ceramic disks [Eheim calls it Ehfimech, Fluval calls it Pre-Filter) go in the first basket of Eheim, Rena, Fluval type canister filters; by first I mean the basket the water first passes through, which in my Eheim and Rena filters is on the bottom of the canister (not sure how Fluval is constructed). These last forever, they are intended to trap larger particulate matter. Of course they support bacteria, but that is secondary. Rinse them when you rinse the filter.
In the next basket after this the biological media is placed, be it Bio Max (Fluval) or lava rock or Ehfisubstrat (Eheim). This is intended to support the bacteria and in Fluval's case it also absorbs ammonia and nitrite, so they claim; I suspect this is minimal. Both manufacturers recommend replacing this media, I never do. It will get clogged with bacteria in time, and I rinse it is hot tap water when I "clean" the filter. I've been doing this for 15 years with no problems. But then I have heavily planted tanks and bacteria is minimal (if it is there at all, in my acidic water). I use Fluval media in my Eheim filters and my Rena filter because it is 1/3 the cost of Eheim's and about 1/2 the cost of the Rena media.