Just noticed Spencer Rifle link...... That's pretty much the stuff.
Here is a link to an related article :
Better than Bleach: Use Calcium Hypochlorite to Disinfect Water | Ready Nutrition
The product on Amazon is just bleach.........read the reviews . Liquid bleach does go bad over time .
I agree with Dudley, keep it sealed, out of sunlight and change of temperatures if possible . Treat it when you need it .
You would be better off making your own " Bleach Stock " from powdered Calcium Hypochloride (78%) It is mainly just stronger pool shock .
Pool shock from Wal-Mart is around 43% I think . ......There are formulas online that explain the ratio to make your own when you are ready for it . 1 pound of it can treat up to 10,000 gallons of water.