If you follow links in a moderator's signature: using the CYA / FC chart you can determine your shock FC value. The pool store is wrong, there is no set amount of chlorine used to shock, it's a process that involves keeping your pool at the shock FC value until it passes specific criteria (also should be linked in a signature).

A partial drain and refill might be needed if your CYA levels are too high (ideal levels are between 40-60ppm)

Temperature doesn't cause algae, un-sanitized water is what allows algae growth.


Remember: the pool store is in business to make money and many people working there might not even own a pool. Also, liquid chlorine is what most people prefer to use.