It is best to prepare MMS1 just before you want to use it (although it is possible to make up a batch to be used throughout the day but you should ensure it is kept in a sealed container to reduce it's degradation over time, as you would with CDS). Chlorine dioxide is a gas at room temperature, and so will gas out of the liquid over time.
MMS1 is made using the two constituents of Sodium Chlorite (Part 1) and Hydrochloric Acid (Part 2). They react chemically and produce Chlorine Dioxide.
To make up an MMS1 solution you should follow this simple procedure. Ensure you prepare in a non-metallic container (eg. a glass, ceramic or plastic pot).
You have made MMS1 and it's all ready to use...