Star San (USA Made): A high foaming, acid anionic, no-rinse sanitizer, which offers no off tastes when mixed in the proper amounts. 1 minute contact time is sufficient for a sanitizing kill level. The foam is a put off for some people, though the chemical breaks down into what is essentially yeast nutrient in your brew.
Concentration: 1 oz/5 gal cold, or luke warm water.
Storage: If DI or distilled water is used to make a solution of Star San, then it can be stored for long periods of time, and will remain active. I keep a filled spray bottle by my kegarator at all times. If the solution becomes cloudy, discard.
A word about chemical concentrations
Increasing the concentration past the recommended levels can have several disadvantages. Firstly, it can take you out of no rinse category, which can effect your brew or your health.
Further, many of the chemicals used in homebrewing, are designed to hit a certain pH or concentration value. Changing the concentration, may therefore reduce the optimal activity of the chemical.
Lastly, excessive use of these chemicals simply costs us MONEY!