Unfortunately, the retail and manufacturing sides of the hobby have different priorities from us hobbyists for the stuff that goes into a filter. For them its important to "move merchandise," to keep up the steady repeat sales of things. For us its all about functionality for the keeping of healthy fish and the ease of use and maintenance.
Filters have three functions: chemical filtration, biological filtration and mechanical filtration. When we all start out as beginners, only mechanical filtration makes sense, it just means "catching the dirt particles." Chemical filtration turns out to be an optional, special thing that we only do when there's need, like removing medications we've put in or other rare occurances. The really important one is biological filtration.
Fish waste and plant debris are broken down in the tank by heterotrophic bacteria that reside in the water. They turn it into ammonia(NH3) and this is a deadly poison to fish. Ammonia, even in small amounts, causes permanent gill damage, leading to shortened lifespan and possible death. The biological media we put in our filters is meant to be the perfect place for beneficial bacteria to grow. It has lots of little crevices they can anchor to and begin to produce "biofilm" which they need to coat themselves with so they can grow and reproduce. The first species we want to attract are ones that can oxidize ammonia into nitrite(NO2) and we like to call them A-Bacs for short.
Once the A-Bacs get going, the nitrite(NO2) gets produced. Nitrite(NO2) is also deadly. Even in tiny amounts, nitrite causes permanent nerve damage because it latches onto the fish blood hemoglobin proteins, just like oxygen, and destroys them. The brain is usually damaged first but other nerves are hurt too and the result is like ammonia, leading to shortened lives and possible death.
On our same biomedia, another species can be grown, which we call N-Bacs bacause they are nitrite oxidizing bacteria. They eat the nitrite(NO2) and turn it into nitrate(NO3) which is much less deadly than either NH3 or NO2. Nitrate(NO3) can be removed with weekly water changes.
So the good biological filtration media, or "biomedia," has the characteristic of huge surface area and is made of a neutral substance and is of a shape that can pack together to also accomplish some mechanical filtration too. The very best biomedia types are sponges and ceramics. The ceramics (like the rough feeling stuff inside a kiln oven, is an example I can think of) are sometimes formed into rings (or sometimes people call the noodles) so that they can "randomize" the incoming stream of water and slow it down so that the particles will settle and be filtered out. They also come as "ceramic pebbles" which can pack together tighter and catch the next smaller size of particles. But all the while, the bacteria that grow on the surfaces of the sponge or ceramic is busy eating up the poisons and converting it into the more harmless nitrate for later removal from the tank. The bacteria grow really well in the filter because the surfaces are right and because there is food (ammonia) flowing by and because the water has a good supply of oxygen due to its steady flow.
All this is by way of explaining WHY we hobbyists like to choose and know about our filter media! Those little Whisper bio-bags do indeed have a little bit of biomedia in them, perhaps a little bit of spongy material. But unfortunately they are really pretty pitiful compared to the big filtration bed found in a typical large filter. And if you take them out and replace them then, just as you may imagine, you are throwing out all your hard-won bacteria that took a couple months to grow! Hobbyists like to keep their ceramic media going for a lifetime and their sponges going for years and years before gradual replacement. So... I recommend you don't replace your whisper biobags, just rinse them in some of the just-removed tank water during your weekend water change so that the debris will be lifted out.
Sorry this is so long but you can save it away to come back and read from time to time and hopefully right after I post this someone will give you the one-liner answer
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~~waterdrop~~
