The Koi Medic Salinity Meter Pen quickly and accurately measures salt concentration in koi ponds. Salt deters algae growth, detoxifies nitrite, eliminates fish parasites and bacterial infections. The tester offers two choices of measuring: percentage (%) or part per thousand (ppt). Extremely accurate and easy to use; simply turn it on, dip it in the pond and press the "READ" button. Within seconds, the LCD displays the salt concentration percentages.