Will running carbon in my canister filter 24/7 have any adverse affects in my tank. I know running it will help with water clarity and stuff (i think!), but i read somewhere in here that it should be used sparingly. If thats the case, why?
I am of the same mind as reefrunner but I use chemi pure instead, also 24/7. May not make that much more difference than GAC but I have liked the results and have not seen anything negative from it's use.
In the end though activated carbon wears out in like a week at most. this is due to its ionic bonding nature which of course will bond to water molecules. Since this is the case you are really just looking at a hosting site for bacteria so really any durable media with a lot of surface area will work.
The main problem with carbon is that the ionic bonds it forms will give up if something better with a stronger bond comes along. For instance those carbon filter masks you wear to help you breath around solvents adsorbs the solvent vapours. But if a stronger ionic bond is present then it will release those vapours for you to breath. And water is a stronger bond than most solvents.
In a fish tank situation carbon can adsorb (not absorb) certain heavy metals, but if a stronger bond comes along then it can release those metals being held. And apparently most medicines can form stroner ionic bonds. So if you use that old carbon to get rid of meds in the water it could lead to the realease of something potentially nasty.
After about a week carbon technically looses its ability to adsorb materials through ionic bonding. But if something comes along that is better at bonding then it will give up stuff that it has already adsorbed.
So what I am saying is that I would only use carbon when I needed to rid the tank of a particular problem. Such things would be getting rid of medications. Otherwise it is just a place for bacteria to grow though the potential for it to unleash something nasty on your tank always exists.