Kevin
If Iron is affected by carbon, therefore running GFO with carbon in the same reactor would exhaust the carbon quite quickly, due to the slow leaching of iron from the GFO?
It would to agree exhaust it more quickly may but have not seen any tests. I do not like that idea at all of mixing any GAC in with GOF par for a slight reason below. I have posted on this many times which has nothing to do with iron.
1.GFO and GAC have very different adsorption rates and you end up wasting allot of GFO.
2. Wasting GAC in the reactor due to any iron adsorption from the GFO.
3. Adding s spoon full of GAC to a GFO reactor as a spacer gor the GFI, to inhibit the "binding/cluing" of the GFO many see. Not that it has to be GAC.
Krish and dnjan
One potential problem with using carbon in a mesh bag is that after a while the mesh bag of carbon can become involved in the nitrogen cycle (after all, carbon is a porous material with a lot of surface area - perfect habitat for bacteria). If you leave the carbon in long enough for these bacteria to start having a significant role in your tank's nitrogen cycle, when you remove it you making a significant change...
This is the main reason I changed mine weekly. Didn't want it to become a little bio-filter. Something people may want to keep in mind who like to run carbon for about 3-4 weeks without changing it.
"Mesh bag"
Should be moved ever week, taken to the sink, water on full blast, turn and squeeze the bag as you turn/rotate it under the faucet to remove any trapped material, which also exposes new ares of GAC plus keeping it from going Bio and replace it 1 / m.
"GAC reactor"
Good idea to do the same, remove and wash it and replaced 1 / m. However, GAC reactors are somewhat self-cleaning due to the slow movement of the GAC grains, so it is not as big an issue as a mesh bag and goes less Bio in the same time as a mesh bag.