HI781 Hanna Instruments HI781 Marine Low Range Nitrate Checker HC Handheld ColorimeterThe HI781 Nitrate Checker HC by Hanna Instruments is a simple and accurate handheld colorimeter that uses the Beer Lambert principle to determine nitrate concentration. The HI781`s low range of 0. 00 5. 00 makes it ideal for measuring the low nitrate levels found in saltwater aquariums. Why are Nitrate levels important? Excess nitrates in a reef system can lead to an overgrowth of undesirable algae and dinoflagellates. Alternatively, not enough