Most RO systems utilize a simple and inexpensive sediment cartridge for the 1st stage prior to the membrane, to catch any possible ferric iron, ferric manganese and/or sediment particles before they can enter the carbon filters and membrane housing. Those solid particles will usually settle within the municipal distribution system, but will often become disturbed and waterborne when there is high water flow velocity such as while fire hydrants are utilized for flushing the water mains or during fire fighting operations or while filling road sweeping equipment.
The 2nd filtration stage is usually a carbon cartridge to remove chemicals that the RO membrane may be less effective to remove, and to remove chlorine which will usually damage the RO membrane.
A carbon block cartridge will be usually installed directly before the RO faucet, to polish the water to further freshen by removing any off taste resulting from the storage tank.
To ensure sufficient capacity and high performance, depending on estimated water production, the filter cartridges are usually replaced on a 6-12 month schedule, and the membrane replaced each 3-5 years.
An inexpensive TDS meter is usually beneficial to compare the TDS of the incoming water vs the TDS of the RO water, to establish how effective the membrane is performing so as to assist to determine when to replace the membrane.
Since your membrane has likely sustained 2+ years of chlorine exposure, suggest replacing the membrane while performing a full cartridge replacement.