There are a large variety of chemicals that can be obtained for use in cleaning and disinfecting pools and spas. These can often provide a good source of chemicals to the home experimenter.
Chlorine shock or chlorine pool oxidizer is calcium hypochlorite, typically from 48 to 65%. This can be used for generation of chlorine gas. Household bleach, a dilute solution of sodium hypochlorite, tends to dissolve most of the chlorine formed when hydrochloric acid is reacted with it. The higher concentration in the calcium hypochlorite allows for the more efficient production of chlorine gas. The remainder is probably inert calcium chloride which does not significantly enter the reaction. Household bleach also has sodium chloride in it due to the similarities of the reaction.
Several chemicals are used to increase the pH or alkalinity of a pool. The most common is pure sodium carbonate. This chemical is useful for precipitating metals as their carbonates. (Sodium bicarbonate may be a better choice for neutralizations and some reactions.) It might be better, though, to buy sodium carbonate as "washing soda", or to simply heat sodium bicarbonate in an oven at 300 degrees Fahrenheit to form the carbonate. To increase alkalinity (and not pH), sodium bicarbonate is used.
To decrease pH, sodium bisulfate is the most common modern chemical. This is slightly more expensive than sodium carbonate, but is quite useful as an alternative to sulfuric acid in beginner chemistry. Hydrochloric (muriatic) acid is also used, although it has fallen into disfavor due to the fumes it releases. This might be easier to find in a hardware store for experimental purposes. Buffered forms of muriatic acid are impure and unsuitable for most experiments. However, it is still possible to find traditional 31.45% muriatic acid to decrease the pH of pool water. Sulfuric acid is also used to decrease pH.
Potassium persulfate (Oxone) is used as a non-chlorine pool shock. The purity is disappointing, only about 33%. However, this is still fine when qualitative oxidation is only necessary. Purer forms of persulfates may be available as etchants.
Sodium bromide is available from two sources. It is sold as a spa bromide reserve in the form of pure crystals. Some algaecides also use sodium bromide.
Copper sulfate is occasionally used to kill algae in pools.
Alum (potassium aluminium sulfate) is used to clear up the water in pools.
Calcium chloride crystals (ice melt) is used to increase hardness in pool water.
Sodium thiosulfate is used to decrease chlorine level in pools.