I am a pool store guy also but I am not trying to sell you chemicals right now. If you get a good test kit that will test both FC and CC, preferably one that uses the FAS-DPD titration test and not the colometric DPD test with a comparator block you will KNOW when you need to shock. You shock when your Combinde Chlorine is over .5 ppm. Every pool is different, you might need to shock weekly, monthly, or hardly ever! Either Cal Hypo or sodium hypochorite is fine for shocking. Cal Hypo can make your calcium levels go up and can cause your water to cloud but it is easier to transport than liquid. Liquid is usually cheaper and readily avaialbe at any grocery store, walmart, kmart, etc. as 'plain unscented regular or ultra bleach'.

There are some of us pool store guys who do 'get it right', btw!