How often change carbon?

[Briko03]

I am running a brs dual reactor with gfo and carbon. I have about 90g of system water. Just curious how often I should be changing it? I know gfo typically lasts a little longer than the carbon.

 

[Ruge13]

For GFO, Every tank is different, depends on variables like the flow rate through the reactor, amount of phosphate in your system etc.
Do you test for Phosphate? If it creeps up, time to change the media. Do this a couple changes in a row and you can get a feel for how long you need to run it before it is expired.

Or, the much less scientific way ... watch your tank... algae starts to grow... change it. No algae spurts, its good. That's more or less how I judge mine, but I change about once per month, or per 1 and 1/2 months. No rhyme or reason other than its usually about time to clean the GFO reactor so I'm already in there and why not.

Carbon I change every other week. Its cheap so why not. As you can see, my advice is highly specific and technical. I don't expect most people to understand.