Sodium Metabisulfite Pickling Solution Mix
With proper care, your reverse osmosis membranes will last for years. Due to the nature of reverse osmosis, the membranes self-clean while the system is in use. However, when the system goes unused for an extended period of time, the membranes need to be "pickled" to ensure bacteria doesn't grow inside and damage the membranes. The powder itself is sodium metbisulfite and dissolves easily in cold water. It is safe and widely used in the food and beverage industry.
This chemical is widely used and available easily from home brew and wine making retailers, among others.
The length of time your system can sit idle without pickling is largely dependent on air and water temperature.