Keep your fish healthy and thriving by testing your aquarium water incessantly with easy-to-use API 5-in-1 TEST STRIPS. API 5-in-1 TEST STRIPS for freshwater and saltwater aquarium assist fish owners measure levels of Nitrite, Nitrate, Carbonate & General Hardness, and pH found in aquarium water. To ensure that fish to thrive, water should be very similar to that which might be found in their natural environment. Poor water quality can cause fish stress, illness or even death. Just dip a strip instantly into your aquarium and use the color-coded chart to resolve if your water is secure, or if adjustments are needed. Then follow the recommendations to treat the water it s that simple.