Gently rinsing the the sponge and the
ceramic media, is good for how long? How often should it be replaced in your opinion? Any thoughts about carbon?
Hello; The sponge and ceramic media are good to house bb until they get clogged up with detritus. If the trapping media is too thin or the trapping media is too porous then the bits of tank trash (detritus) get by and into the bio-media
(bio-media = solid surfaces often in filters meant to give a place for the bb to colonize. My take is bio-media can be pretty much anywhere there is some water flow. The greater the surface area equals more surface for the bb the form a bio film. That way more can be packed into the available space.
Seems to me that the porous nature of some bio-media will likely get clogged up over time with fine detritus. I used some carbon back in the 1970's that was not very dense meaning it was porous. I would bake it in my oven in the erroneous notion I was re-activating the carbon. I have since learned a home oven does not get hot enough to re-activate. It did however bake away a lot of the organic stuff that had clogged up the spaces in the carbon. That made the carbon a decent bio-media that was a bit more cleanable and I could reuse it several times.
I suspect ceramic media that is only gently rinsed off from time to time will lose some of the available surface. Not sure how to go about cleaning the clogged spaces.
A sponge can be simply squeezed a bunch of times in water to clean out a lot of the detritus. Likely should be squeezed out fairly often)
Ceramic bio-media ought to be useful as long as it is in good shape. I have not used it so cannot say how long it stays in good shape. Back a few decades ago when none of the current choices were available I used small glass marbles. Not porous but they packed fairly tight and allowed good water flow. They were also easy the rinse.
Another thought - The bb make a sticky bio-film which clings to a surface. It is my understanding a simple rinsing does not wash it away. I suspect a scrub brush will get it off exterior surfaces. I think the term is sessile to describe how it sticks to surfaces. The bb can and likely will be on surfaces thru out the tank.
On carbon. Activated Carbon has the property of adhesion rather than absorption. That property makes it useful for only a brief time. It is good for removing chemicals such as medicines after a tank treatment.
In adhesion a chemical molecule is picked up by the carbon and bound very tightly. The carbon can only pick up and bind so many molecules and then it is "full" so to speak. This could take only a few hours or days and the carbon is full.
I think of it sort of like carbon monoxide and carbon dioxide being picked up by the hemoglobin in our blood. Red blood cells can pick up CO2 in our bodies and carry it to the lungs where the CO2 can be released. However when a red blood cell picks up carbon monoxide (CO) the cell cannot release it at all. That red blood cell will become useless and will circulated thru our bodies until it dies and is replaced.