Carbon can be used on a reef or Fo
The use of activated carbon in marine tanks is considered to be a form of chemical filtration. Working through absorbtion, GAC
removes gelbstoff (the compounds that give water in an aquarium the yellow tint), some large organic molecules, medications, chlorine, pollutants and toxins, as well as many other types of chemical elements and compounds from the water that a protein skimmer or another means of filtration may not remove. This is from a web site..... Too much for me to type....
I use it every few months to clean the water if it looks dull. Other guys in my reef club run it every month. They have great success with corals so I see no harm in running it. It all depends on your tank when to change it, there is no set answer on how long to run it. I would not run it longer then a month so there is no leach back into the tank.
Is the canister needed no, will it hurt the system no. You can use it to run carbon when you want to or just us it for added water flow. You can use a filter pad in there from time to time to really clean the water also.
Clean the filter pads on a regular basis.