It is really simple. first you need to buy the right test kit -- trust me on this.
I have no idea on how people take care of their pools anymore blindly, without a kit. My friend who used to go to the pool store now comes to me for testing. He does have the basic kit, but weekly, I will run a few tests for him. His pool is now crystal clear and has stopped using 3" tablets. Now using liquid chlorine. His CYA was at 60 and with limited circulation, algae started forming. The strange part is that for over 10 years he has had algae issues. I have not seen a trace of algae since TFP.
Your own testing is necessary (bottom line). Yes, while it may be tempting to wait in line at the pool store and watch everyone walk out with hundreds of dollars worth of rebranded Borax, Baking Soda, Clarifiers, shock, phosphate removes, algaecides, and other chemicals to clear up their pool (This is why they are there as a problem exists)., I have better things to do.