The test strips you need will depend on the whether you are using chlorine or chlorine free chemicals.
If using BioGuard Armour Spa Sanitiser, the test strips test for Bromine, Chlorine, pH and Alkalinity. For example BioGuard Test Strips 4 in 1.
If using Hydrogen Peroxide, the test strips test for Alkalinity, pH and Calcium Hardness. For example Poppits 4 Way Test Strips.