08-01-2012, 09:37 AM
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I stopped using carbon years ago, but...
How often you have to change the carbon is largely a function of your water change schedule - the more water you change, the more often you will have to change the carbon in order to maintain "effectiveness". A month is a good guestimate, and very convenient, but you ought to adjust it based on your specific situation. We look at it as a matter of time because that's easy to gauge, but since there are a finite number of attachment sites, it's a matter of volume of water to be filtered that dictated the schedule. Every gallon of water added to the tank has X amount of stuff in it to be filtered
There is a lot of misinformation out there about activated carbon. Carbon works via the van der waals force, which means that no real chemical reaction takes place. Some things have a higher affinity for the carbon than others, which means that when the carbon is full, it will begin to leech things back into the water - that is not a myth. When it is full, something with a higher attraction to the carbon will bump out something with a lower attraction, and that is what gets released back into the water. Generally, the things with the highest affinity are the most dangerous. Activated carbon will NEVER spontaneously release all that it has adsorbed - it requires a temp of 700 degrees C in an oxygen free environment for it to be recharged.
I always clean my media in tap water and never have minicycles. The established bacteria colonies are much more resilient than most people give credit for. The tap water does not sterilize the media - a quick rinse of the biomedia is all that;s needed to "clean" it up, which leaves the bacteria in tact. I thoroughly wash the mechanical media - even then, what remaining bacteria is on the sponge will quickly repopulate it. I would not suggest this for a newer tank, but there is no fear with an established one.