How often do you change media in your carbon reactor?

I just installed two Phos Ban reactors in series. Once for carbon, and the other for GFO. I plan to change the GFO whenever my phosphate tests show that it's not working anymore.

I'm wondering how often I should change the carbon. Previously, I was running carbon in a media bag in my sump. I was changing it every 3 weeks.

I currently have 5 LPS, 2 soft corals, and only 1 SPS in my tank. The SPS was a free frag given to me by my LFS to see how my tank would handle them, and it's been doing okay so far.

I have a 110 gallon tank with a 30 gallon sump.

I'm know that the reactor makes the carbon more efficient than running it in a media bag, I'm just wondering if that translates into having to change it less often

 

I change mine once a month.. I used to change it twice a month and also run GFO but I have not had any problems in a while..

 

I do mine every two months...