It would be helpful to know ...
Published by Derek French, Wateropolis Inc. - Founder
It would be helpful to know what the "iron removal filter" is. If it is Mn02 based media (greensand or pyrolusite) then the chlorine must be dosed before the iron removal filter. The chlorine is very capable of oxidizing the iron effectively prior to filtration. If the "iron removal filter" is not chlorine compatible then move your chlorine injection to up stream of the sand filter.
Most likely you have ferris iron leaving the iron filter, going to the end of the treatment. It may then oxidize once you add chlorine and give you additional ferric precipitation.
The downside to this is that you would need to re-inject chlorine after the carbon for a residual. If the carbon is not being used for DOC, T/O or VOC's you may simply be able to eliminate it but i would need more water quality information.