The bed could be getting close to needing a change out, one good sign is the with the water at the same quality and usage the same the system has to go more often for the water to be treated.
Yours would be about 10lbs of fine pea gravel or some thing along the line of #20 and then about 1 cubic foot of carbon, at least I think that is what culligan uses in systems like yours.
The amount would depend on the size of the media tank under the control that you have worked on.
Ill have to check the manual to see if it says in there. I didnt know if it was specific to the unit or specific to my water.
I see now why you said there would be two pieces to the injector assembly. I was pulling out the injector, not the injector and holder.
The media tank is most likely 10" across and 47" high?
It is good that you are learning about the parts on the system.
Actually its 10" across by about 54" tall.
With the 10x54 that would be 1.5 cubic foot of carbon and about 13lbs of the very small gravel.
Now my thought would be that you the owner has a right to know the media that is in use, not the Corp name like Culligan but the data sheet and the street name of the media.
It could be that they are using the Centar Carbon... little spendy but good and if your system has gotten a number of years... say 10 then I would stay with the same type of carbon... it should be cheaper than the Culligan bags ....
The media for these tanks is Centaur Carbon. If it is the newer style with a center opening tank then you simply need to dump out old media, add gravel bed and appropriate amount of centaur (1 1/2 cu ft for 10x54 tank), being careful to not get anything down the distributor tube/manifold. If its the old style tank it would need to rebed by the dealer.