What chemicals are used to start up pool for the second season?

Depending on your size pool when you are first opening I would suggest using a couple gallons of liquid shock and a non foaming algaecide to start. These should be dispersed one at a time by walking around the peremeter of the pool while the pool filter is running. Let the filter run for 24-48hrs and then test your water for PH, Alkaline, Hardness and Cyanuric Acid. I usually tell my clients to wait the 24-48hrs so that if you have to do a lot of vacuuming hence backwashing you are not backwashing your money with the water so before adding a bunch of chemical try to do at least a good 1st vacuum. More pool tips at www.prospectpoolslllc.com/blog