Struggling to control nitrites / nitrates

[RobW]

Also look into the microbacter clean. It can be used in conjunction to help clean up the tank. I've had success using it.

 

[Viking_Reefing]

Like others said the carbon won’t do you any good after such a long time, you generally want to change it about every month or so.

How’s your flow? Is is possible that there’s been accumulation of crud between your rocks?