Yes, media takes some learning for beginners and then has aspects we all keep learning more about over the years. Many experienced aquarists pride themselves in having media that runs for decades - that's what the competition is all about between things like sponges, ceramics and pot-scrubbers, so see which ones can last the most decades while doing the best job.
As GVG said, sponges will last many years with just regular rinses in tank water at the needed interval when the filter is being cleaned. The bacteria are like a brown stain tightly bonded to the media surfaces, so dunking and squeezing to loosen and removed organic debris will not lower the bacterial counts by that much. Ceramic rings or chunks or gravel will have their debris removed when the media tray is dunked and swished in tank water.
Carbon (aka activated charcoal) is best kept on the shelf for special needs. It removes medications, yellow wood tannins and the rare organic odor of unknown origin. When put in the filter it lasts about 3 days, after that it is no longer performing chemical filtration in most cases and after a couple of weeks will begin to clog with organic debris, as GVG mentioned.
The -replacement- of carbon and sponges with new ones is usually undertaken by people who don't yet understand biofiltration and is promoted by entities hoping to make money on a regular basis. Years down the road, when you do end up making a change, you usually do it in fractions, perhaps 1/3 of a sponge at a time, by cutting both the old and new ones with scissors. The 2/3 mature sponge that remains will seed new bacterial colonies in the 1/3 new piece that replaced the removed part.
In your case, a black "carbon impregnated" sponge is not really a bed of carbon and there's no problem just keeping it for use as a "sponge." (Sponges, like most types of media, fall into more than one category of media: the serve as both biomedia and mechanical media (and in your case, chemical for the first 3 days, lol.)) Ceramic rings and coarse sponges excel at large mechanical filtration (trapping of larger particles) but also have a biological component in that their surfaces also make good places for bacteria. Ceramic gravels and plain gravel beds can serve as good biological media, like sponges. Pot scrubbers (avoiding any that are pre-soaped of course) and "bioballs" (balls composed of plasic rib structures) make good biomedia in large filters and sumps because they have a lot of surface area but avoid clogging over long periods. They are less efficient of space in medium to smaller filters, where ceramics or sponges are probably better (well, bioballs are less efficient than pot scrubbers in this regard.) Polyfloss, either like cotton or in pads, is used for fine mechanical filtration and is the one media type that is often tossed and replaced when it starts to break down. A filter should have enough true biomedia that the loss of a mature floss pad has no effect on biological filtration.
A filter is a very interesting thing. You want to clean it at regular enough intervals that good flow is maintained because the bacteria need fresh oxygenated water, in addition to their supply of ammonia, which they get both from the new ammonia constantly flowing in and from the ammonia being produced within the filter as the heterotrophs break down the organic debris trapped in the filter. And yet you also of course want filter media that does a good job trapping debris, so that good trapping ability is working against your desire to keep things clean and flowing. This is why regular maintenance must not be neglected.
We have two indicators that help us know how often we should clean our filter. The first and most obvious is reduced flow. This always trumps other habits. If you notice reduced flow then you need to clean. The second indicator comes from our aquarium notebook (which of course we keep daily, right?) Here, we scan down the page and look at our regular nitrate(NO3) test results and see whether they seem to be holding steady or are trying in increase a lot on us. It takes time to get a feel for this for a given aquarium (and especially if you are in only your first year or two of being an aquarist) Generally, we'd like a tank to balance at a max of 15 to 20ppm -above- whatever the tap water nitrate(NO3) reading is. It's not terrible if it's worse than that as long as it stays steady.
Nitrate(NO3) is our "canary in the coal mine" chemical test. Each week we test it and remove it with the weekly substrate-clean-water-change because we don't want a nitrate buildup, BUT also because there are hundreds of other substances we want to keep from concentrating and nitrate is just "symbolic" of those other substances (ie. we know they too are building up but we don't have the time or money to test for all of them so we use nitrate as our "canary.") [By the way, for folks you may not have heard that saying, the canary stops singing and sometimes dies if there are poisonous gasses released during the mining, warning the coal miners to quickly get out of the mine.]
OK, hope that's a filter media post you can come back to if you want to be reminded of things and that it perhaps helps you a little with your current questions.
~~waterdrop~~
) WD
