Yeah, I understand that. But for infectious bacteria to grow on the carbon it would have to first be introduced to the aquarium. After that any bacteria that would grow on the exhausted carbon are just as likely to grow on any surface of the entire tank. Microbes aren't going to specifically select carbon as their source to grow on, they will grow wherever they land.
Here's what one of the "senior moderators" from
KokosGoldfish.com was absolutely certain on with regard to the exhausted carbon issue; this has been clipped verbatim from a conversation I had with him on there...no changes or alterations to the context have been attempted:
1. Were it not for the carbon, the rest of the media is just like the DIYs, you can rinse it and reuse it until it falls apart.
2. I am not one to disregard carbon's importance and use. However, it's really not necessary. Unlike some myths that get passed around, "loaded" carbons do not release back to the water what they once held. Carbon however, can contribute to the increase of phosphates in the water, and that will depend on the brand. Some will have more than others.
In statement #2, he is suggesting that
phosphates can be introduced into the water column via exhausted carbon...
3. The real problem is that Aeromonas, a group of pathogenic bacteria, love to colonize in these carbon particles. The longer you leave them there, the more these will grow and can attack your tank. Aeromonas' effects on goldfish include fin problems, ulcers, and wen ulcers.
Here, in statement #3, is where he is attempting to suggest that these "Aeromonas" are colonizing in the carbon and that if left too long, can "attack" the tank -- he goes on to describe effects on goldfish, one of which my Moor seems to be exhibiting, hence my overall concern here...
He cited some research on two different sites to support this, but the links apparently expired or were "broken"/corrupt...
However, he went on to say this about one of the points made in this research:
Point 3 is the reason why I vehemently oppose the use of carbon long term. It's not necessary. It's expensive, AND it can bring disease to your tank.
Now, this was the second round of communication with him:
What I am suggesting is to dispense with carbon entirely. I have not found any convincing arguments as to why they need to be there. From the stand point of having replace them often (every month according to the companies suggestions), to them taking up valuable real estate that could be occupied by other media, to the fact that they can harbor pathogens, to the fact they can leech phosphates all argue against using carbon.
Again, he is suggesting, via this statement in red, that something is most likely being leached back into my tank in the form of "pathogens"...
The answer to your question is that no one knows quite when they are exhausted for your system, unless you test it. The companies suggest 1-2 months (depending on the product and the company), but that's really an estimate, and I'm not even sure how good that is.
This above statement is merely in response to something I was asking about exhaustion rate; not really related to anything with regard to the pathogen angle...
Now -- the below was the third round of communications I had with this individual:
There are many scientific articles showing about Aeromonas living on the carbon particles, as well as the fact that it leeches phosphates, which are also undesirables in the tank.
Again -- he seems extremely certain from this red-outlined statement above that scientific backing suggests these Aeromonas WILL live on carbon particles and WILL attack things in the tank...
Could those bumps/cysts be bacterial? Could they be from carbon? Probably. Why can't I say for certain? Because I don't have anyway of having you test for the presence of Aeromonas there, but the symptoms are consistent with Aeromonas driven diseases. More than that, and we would require some microbiology work.
Here, he's blatantly saying he believes it's probable my Moor is exhibiting these symptoms directly because of the exhausted carbon and the "pathogens" within...
Your last question brings to mind another reason why cartridges are such a terrible idea. Every time you do this, you remove beneficial bacteria, since you are throwing the cartridge away. So, it is the clicheic throwing out the baby with the bath water.
Yes, replace them if you suspect that it's causing you problems. Switch to media that have no carbon.
With regard to his first statement in the dual paragraphs above, I explained to him that with these Aqueon cartridges, beneficial bacteria is not always necessarily "thrown away" by the disposal of the old cartridges because of the "bio grids" these filters come with and which are supposed to house at least more of the bacteria than what's on the floss pads...
But his second statement there suggesting I swap out the cartridge(s) is what concerned me and thus lead me to swapping out one of them the other day for a new one...
What do make of his analysis here?