I think you should disconnect the other two and monitor nitrates. I don't know what the missing thing is that stops the bacteria from working but it is something corals need to because they get unhappy or dead. You can always hook them back up if nitrates spike upwards and then wean your tank off of them if you have to. You probably should monitor ammonia also just in case.

Mark is still being a trooper (for now) and trying various Snake potions to try and figure out what missing thing is without doing massive water changes. It definitely isn't that the carbon is old since he replaced his with no effect.