R1 is a high performance mixed bed ion exchange resin.

It consists of a mixture of two polystyrene gel resins:
- a strong anion resin
- a strong cationic resin.

It has a high degree of phosphate and other residual anions (silicate, arsenate, vanadate, borate, etc.) removal and an output conductivity of less than 0.1 μS/cm (micro Siemens on centimeter).

The resin must be inserted in a post-osmosis stage to break down the residual conductivity (in particular in order to absorbs phospates and silicates) passing the osmotic membrane.

To this end, the resin must be placed inside a refillable cartridge (for example:https://www.alxyon.com/shop/en/reverse-osmosis/empty-cartridge-for-ro-systems.html), which is placed inside an inspectable vessel (for example: https://www.alxyon.com/shop/en/reverse-osmosis/reverse-osmosis-filter-vessel-10-pp-transparent-eu.html).

The vessel containing the resins must therefore be placed as the last filtering stage; at the outlet (in series) to the osmotic membrane.

In a properly designed and functioning osmotic system, the conductivity leaving the osmotic membrane (before entering the resin stage) should be a few μS/cm.
Ideally under 10-20.
And the conductivity out of the final resin stage should be 0 (ZERO).

The activity/efficacy of the resins must be monitored through the use of a correctly calibrated conductivity meter and the resins must be replaced when the conductivity leaving the system returns above the limit value considered tolerable for the type of use or close to that in exit from the osmotic membrane.
Alxyon recommends replacement when conductivity rises above 10-20 μS/cm