Read all instructions carefully.
Always add chemical products to water and never water to chemicals.
Never mix chemical products. Add products individually. Rinse the measuring cup before adding the next product.
Store chemical products in a cool, dry place away from children.
In case of skin contact or ingestion, follow the directions on the label or contact a poison control centre.
Do not smoke near chemical products. Keep unused containers closed securely.
Also, you can consult the page from Health Canada "Consumer Product Safety - Your Swimming Pool and Spa".