Features Measures total and free ammonia down to less than 0.05 mg/L Multi-cavity plate for simultaneous testing of up to 6 tests at the same time Includes reference for test validation Marine or Freshwater This kit measures total (NH 3 and NH 4 +) and free ammonia (NH 3 only) down to less than 0.05 mg/L and is virtually interference free in marine and fresh water. Free ammonia is the toxic form of ammonia (vs. ionized Ammonia NH 4 + which is non-toxic) and thus it is much more important to keep an eye on the level of free ammonia in your system. This kit may be used with freshwater or marine water. Unlike other kits on the market, the chemical basis for this test assures that interference from other substances is highly unlikely. MultiTest™ Ammonia performs over 75 tests and contains a reference sample for validation. Features 75 Tests - MultiTest™ Ammonia performs over 75 tests And with the multi-cavity test plate, multiple tests can be run at the same time. Seachem Sensor Technology - This kit is based on the same gas exchange technology that is used in the Ammonia Alert® and thus is the only kit on the market that can read levels of free ammonia while using ammonia removal products such as Prime®, Safe™, AmGuard™ and any similar competing products. Other kits (salicylate or Nessler based) determine the total ammonia by raising the pH of the test solution to 12 or greater. At this high pH all ammonia removal products will breakdown and rerelease the ammonia, thus giving you a false ammonia reading. Reference Sample - It isn't necessary to run a reference test to use this kit; however, its proper performance can be validated by running a test in the normal manner except that the reference sample is used in place of aquarium sample. You might choose to run a reference test if you have cause to believe the test is giving incorrect results. Color Chart All MultiTest™ test kits come with an easy-to-read color chart. It features a 5 cm viewing window to help isolate color and match as closely as possible to the test sample Opaque Multi-Cavity Test Plate All MultiTest™ test kits are read from an opaque white test plate. The sliding color chart along with the six-cavity test plate allows for easy reading and comparisons of several samples at the same time. The best HTML CheatSheet has its own visual editor where you can apply your own CSS code as well. Web developers and designers love this free online resource!