The HI780 Checker®HC (Handheld Colorimeter) is a simple, accurate and cost effective way to measure pH in saltwater. PH is a measure of the hydrogen ion concentration in your water; the higher the concentration, the more acidic the water is. A neutral pH is 7; most fish can live in a general range between 6 and 8. Keeping your aquarium pH stable and in optimal ranges reduces stress on your fish and aquatic animals, helping them resist disease and tolerate other stressors. Maintaining an ideal pH can also dramatically improve growth, behavior, and overall appearance.