A good pH meter would be waterproof and have a range between 0-14, with a 0.01 resolution.
Some pH meters also include a particle meter, which measures the density of the solution, and a thermometer to measure the water temperature, which is ideal for mitigating spirulina growth.
The pH meter measures the difference in electrical potential between a pH electrode and a reference electrode. It usually has a glass electrode plus a calomel reference electrode, or a combination electrode. In addition to measuring the pH of liquids, a special probe is sometimes used to measure the pH of semi-solid substances.
Browse our shop for a selection of pH meters