WHEN TO SHOCK AND WHICH SHOCK TO USE

• IF THE WATER IS GREEN
• You need to shock, no doubt about it, BUT FIRST, make sure that the total alkalinity is between 125 - 150PPM (for pools with a liner or concrete), 100 - 125PPM (salt or fiberglass pools), and that the pH is at 7.5, otherwise, the shock will not be as effective as it should, if at all.
• Use a concentrated algaecide, IE 50% or more and granular shock.  The greener the water, the more chemicals required.

• IF THE WATER IS WHITE
• You probably need to use an oxydizer and not a shock - It's the organic matter (from bathers) and chloramines (chlorine residue that smells and stings) in the water that make it cloudy or whitish.
• 1 bag per 40,000L - 15 minutes waiting time, that's all.

•  IF YOU ARE USING GRANULAR CHLORINE (CALCIUM HYPOCHLORITE MORE EXACTLY) WHICH IS CHEAPER AND AVAILABLE EVERYWHERE
• Then it's the calcium in it that didn't dissolve.
• You need to add a clarifyer and it would be best to change to trichloro chlorine which has no calcium in it.