Welcome to FishLore! Testing is very important. A lot of times, it's the first indication of what's wrong with your tank, and your why your fish are acting strange. There are a lot of different tests out there. The strip tests are the easiest to use, but more expensive and commonly inaccurate. We recommend here on FishLore the Aquarium Pharmaceuticals Master
test kit because it is economical, and accurate. You really need to do your own testing. It seems there is always a problem in the tank when the stores aren't open.