Chlorine

• Chlorine is an essential chemical to add to your pool when you first open it for the summer to kill any bacteria that developed through the winter months. Large amounts of chlorine should be added to the pool as soon as it's opened, typically around 3 to 4 gallons and only as needed after that. Chlorine comes in liquid, granular and tablet form. The pool is safe to use when the chlorine level is below 3 parts per million (ppm) and the water is clear.
  
  

pH Chemicals

• Pool pH chemicals are designed to balance out the water's chemistry and keep it safe to use. The chemicals are used to reduce the scale that may form along the pool walls. Pools should have a pH level between 7.4 and 7.6, according to Pool Center.com. If the levels are too acidic (below 7.4), use soda ash to increase the pH, and if the levels are too basic (above 7.6), use sodium bisulfate to decrease them. To test for these levels, you should purchase a test kit from a pool supply store.
  
  

Alkalinity Adjusters

• You should also perform a test for your pool's alkaline levels, which will show how much alkaline materials are in the pool water. If you find that the alkaline levels are too high, use a pH decreaser or sodium bisulfate. If the levels are too low, you must use a chemical known as an alkaline increaser, such as sodium bicarbonate.
  
  

Algaecide

• Algaecide is a type of chemical that kills any and all types of algae that may form in the water of your pool. This type of chemical is especially helpful for opening up a pool that was not properly winterized. It kills the algae, cleans the lining of the pool and removes any odors left behind from the algae.