There are two membranes to choose from, this Cloth Membrane used in the G-2B and G-2C, and the older ball fiber membrane. This is a flat cloth membrane that fits on the end of the pipe, and is recommended as a replacement for the ball fiber membrane. It produces a higher ORP output in less time, and has less problem with mold growth since it will dry out quickly. It is made from organic cotton.
You MUST use with the newer 32VDC power supply (or 36VDC on the G-2C). The original 24V power supply will be overloaded and use will void the warrantee. (Read the label on your power supply if you are unsure what you have, 24V or 32V or 36V). If you don't want to upgrade the power supply, continue to use the older ball fiber membrane.
If you are doing an upgrade to the G-2B, you also need to purchase a Replacement Retaining Ring if you do not already have one.
You will need to use both bottle lids to properly remove the water from the ionizer when using the Cloth Fiber Membrane (the ball fiber membrane only requres one lid). And, you should download the latest user manual for version G-2B or G-2C.