How often should I be changing out carbon?

[malawian]

I go for monthly, with the knowledge it does very little for most of that time. with that in mind i try to use a little bit less than most would probably recommend so that when I change it out theres not a sudden "spike" of changing water parameters. Mainly Im trying to avoid the gradual buildup of nasty things that may get accidentaly introduced into the tank because I've had experience with the "once you notice a problem its already too late" idea (of course its not completely too late but at that point something has already gone "wrong" IMO and now its harder to fix). I also let my carbon tumble (somewhat aggresively actually) because it doesnt get broken into dust within a month anyway and the little bit of dust it makes will have the highest surface area of anything you could imagine (a fine powder of activated carbon would be almost ideal). My HOPE is that this will also help to decrease SOME bacterial colonization since most bacteria prefer a low flow.

[Nocturnal]

recently researching similar question. I thought this was a great link: http://www.theaquariumsolution.com/rowa-carbon-question'>http://www.theaquariumsolution.com/rowa-carbon-question

 

"In general, all carbons used in salt water have an absorption curve that peaks rapidly in the first 24 to 48 hours. Adsorption then drops off gradually over the next 10 to 14 days, partly due to the media becoming more saturated with bound organic dies and dissolved organic compounds, but also due to increasing bacterial colonisation which gradually fills the porous structure limiting further uptake. By day 14, the carbon is effectively useless.

 

The two day recommendation is based on the premise that after 2 days, the carbon isn't performing at peak levels and has done most of its work so can be removed. And that an average aquarium will happily function for several weeks between carbon usage.

 

In the USA the alternate method is to use larger quantities over longer periods, swapping it out for new media every 10-14 days maximum. This method is based on the idea that it is better to run carbon constantly rather than intermittently, to increase long term system stability and to avoid gradual increases in organic dyes etc between changes. But this isn't a method that should be initiated in one quick change as it may shock some sensitive corals if water clarity is suddenly increased allowing greater penetration of intense lighting. So the trick is to build it up slowly if you are going to use this method. What happens over time is that you get to a stage where the amount of organic dyes present in the water as well as other dissolved organic compounds are at levels low enough that they don't saturate the amount of carbon you are using so quickly, so the adsorption curve is flattened out over a longer period because the carbon isn't limited by its capacity any more, it is now limited by the 'availability' of material it can sequester from the water. But the bacterial colonisation rule still applies, so at day 14 maximum, even if the carbon isn't saturated, it will be blocked by bacterial growth so will need replacing."

 

 

 

Good stuff. I had no idea that carbon tapered of so fast.

[seabass]

Different activated carbon performs differently:

 

BRS recommends changing out carbon every two weeks:

If you are mixing GFO and carbon like in this video, simply use less GFO so that you are not wasting it by changing it out every couple of weeks.

 

I also feel that changing out your carbon every two weeks is best. While there are a number of variables which will affect the life, like Polarcollision posted, it will be the most effective in the first two weeks (and pretty much totally spent in 30 days).

[Nemo22]

So is it pretty unanimous that leaving the carbon in the sump after a window of 2-14 days is actually bad for the reef? Or can old carbon be left for longer periods, even if it's usefulness is in question?