The HI774 is a cost-effective way to measure phosphate in marine systems, including reef tanks. Testing for phosphates is standard practice for saltwater aquariums and provides valuable insight into your reef tank's water chemistry to help ensure long-term coral health. Phosphates are one of the many forms of phosphorus compounds found in marine waters. Excessive phosphate levels can prevent calcification, skeletal formation, and growth of many coral species, particularly those referred to as SPS or small-polyp stony. In addition, high phosphate levels can cause nuisance algae growth in your reef tank. This can become problematic because algae often outcompetes sessile organisms for light, nutrients, and space, jeopardizing long term coral health in your reef.