Guardex 4-In-1 Test Kits have been the standard of the industry for decades. The 4-In-1 Test Kits test for chlorine/bromine, pH, alkalinity and acid demand. It is available with either DPD (Red Box) or OTO (Blue Box) as the method to test sanitizer levels. The DPD version has the added benefit of being able to test both free and total chlorine levels.