Product Description: HM Digitals PH-200 is a digital waterproof pH meter (aka pH tester or pH pen) that is ideal for all pH testing, water purification applications, wastewater regulation, aquaculture, hydroponics, colloidal silver, labs & scientific testing, pools & spas, ecology testing, boilers & cooling towers, water treatment, wine, coffee, agriculture and more. It is fast-acting, features amazing results and perfect for the hobbyist to the laboratory professional.