Yes a second inline filter.
And the one in the unit should be replaced at least every six months.
The link below is to the part you will need from a highly recommended company rated A+ with the Better Business Bureau.
They offer a 100% money back guarantee, EVEN ON INSTALLED ELECTRICAL PARTS, for an entire year!
They are the only company to allow returns on installed parts for a refund and offer a FULL ONE YEAR WARRANTY!
This is the coiled water line behind the crisper area.
This is the water line under the unit from the water supply valve to the water filter housing .
This is from the filter housing back to the water valve
This is the water filter housing .
This is from the water valve to the icemaker
this is from the water valve to the chilled dispenser inside the door .
Your water system comes into the refrigerator from the rear it goes into the dual water valve one goes to the filter housing into the filter ,then out of the filter to the chilled water reservoir then to the chilled water in the freezer door.
The second part of the DUAL valve goes to the icemaker inlet .
If you have any questions just reply back to me .