The Fluval A7840 is an aquarium water test that tests the level of the following in your aquarium water:
The Fresh & Saltwater Phosphate Aquarium Water Test helps to detect high phosphate levels which can contribute to algae growth. Phosphate levels should generally never exceed 1 milligram/Liter (mg/L). This aquarium phosphate test helps keep your aquarium water comfortable for your fish. This water phosphate test is suitable for use with fresh or saltwater tanks.
The Fluval A7840 specifications: