Manny - you can use those cartridges but you need to be religious about cleaning them/changing them so bacteria doesn't build up. Looking at the amount of live rock you have I am thinking the system is relying on the bacteria growing on these filter pads for nitrogen breakdown and when you remove it the tank is temporarily thrown out of whack and a bacteria bloom accompanies it?

Try getting another 10lbs of rock and seeing if that works. Also what I often do is just take the filter pads out and put small chunks of live rock rubble in the filter compartment - worked real well on my little eclipse filter and I have done the same with a fluval canister filter and an aquaclear.

Carbon is beneficial but I wouldn't run it all the time. If you want to 'recharge' it I know we used to bake ours in the oven to recharge it back in the dark ages (10+ years ago).