Virbac Mardel 5 in 1 Test Strips for pH, hardness, alkalinity, nitrite, & nitrate, for saltwater and freshwater aquariums. 5 in 1 Indicator: pH indicates if your water is acidic or basic. A stable pH is critical to a healthy aquarium. Alkalinity is a measure of the compounds that stabilizes pH. Hardness is principally a measure of the calcium and magnesium in your water. If water conditions are not within the desired range, your fish may become stressed and susceptible to disease. Note: When fish species from different locations are kept, a tank is referred to as a community tank and a general range of conditions are recommended. Nitrite & Nitrate are byproducts of the nitrogen cycle, a natural process that breaks down waste in aquariums. Nitrite is more toxic than Nitrate, and should be held below 1 ppm. Mardel test strips use the same technology found in medical laboratories and replace other potentially toxic and time consuming kits. They are designed to be accurate and dependable while being safe and easy-to-use. Contents: 25 strips and water quality guide.