This is the replacement resin for the AR PRO and DI pure water systems.
The resin is a 50/50 mix of cation and anion resin, which ensures that the resin will remove all of the impurities from the water to show 0 PPM on the TDS meter.
It is available in options of 5L and 25L, so you can keep it in bulk for quick resin replacement when it is needed.
Be sure to keep the resin in an airtight container so it stays fresh.