Life of Eheim Canister Filter Media

I'd just fill it with Ehfimech or similar ceramic noodles.
Check http://www.tomgriffin.com/aquamag/cannister.html

You shouldn't need anything at first. They come with media. My 2217's came with the media. I've had mine for 8 months and cleaned them twice. Depends on how many fish you have and the amount of debris. When you notice your water flow diminishing, then its time to clean.

I don't know anything about the 2215 CLassic, but I'd probably go for the 2026 Pro II just for the self priming aspect. Some of the older Eheims were a bit of a challenge to prime. I'm running 2 2028 Pro II's and they set and prime very easily.

The Eheim 2026 will be much easier to maintain and is a more durable design, although in the long run you will want to use just ceramic noodles and bioballs, as opposed to the proprietary stuff that Eheim sells which unfortunately loses much of its effectiveness after a relatively short period of time.

The Eheim canister "system" relies primarily on little nuggets of sintered glass which grind against each other and macerate the detritus so that theoretically it breaks down faster. Their polyfiber media is primarily intended on intercepting the little pieces of broken glass before they get back into your tank. And all of the above clog and lose much of their biofiltration capacity after 6 months or so (probably there's some variation in there based on the bioload of your tank and whether or not you use a prefilter to keep goop out of your filter, but I've never really experimented with it to know exactly).

Anyway, replacing this specialized media can cost you up to $100/year, which does nothing but enrich Eheim unnecessarily. RTR (a prime proponent of Eheim filtration on these boards, if not the actual high priest; I myself use Eheims and Fluvals interchangeably and am thus somewhat more, um, ecumenical in my approach) has, in previous posts, recommended Duplakascade bioballs and ceramic noodles as a better media combination, and one that never needs to be replaced, to boot.

Harry Tolen do you something to seperate the ceramic noodles from the bioballs in your filter or do you simply place the bioballs on top of the noodles?

Where the filter has baskets, I use 'em. But some of the older Eheims don't (for example the 2260, which is still my workhorse for larger tanks). When there are baskets, I simply remove them and dump buckets of tank water through them until they run clear; when there are no baskets, I manually remove the bioballs, rinse them in tank water separately, and then dump water over the noodles still in the filter until the remaining detritus runs out the bottom valve.

You only need to replace 1/3 of ehfisubstrat each 4-6 months or so, more like $12-$15 year. The other filter material is nearly permenant or inexpensive.
I like the idea of permenant substrate, but they still don't provide the bacterial colony density that ehfisubstrat provides.
The gravel nuggets (sintered glass) are not meant to grind together to break up deitrus, that what noodles are for.
I seperate my noodles from substrate with coarse pad or ehfifix.
As for 2 inches each, that should be adjusted to your needs but is a good place to start.
good luck