Our handheld and portable TDS, EC, pH and ORP testers, in-line monitors, controllers and accessories for reverse osmosis (RO) water filters, water purification systems, hydroponics, aquariums, pools and many other applications are superior in construction and performance, yet made available at a very economic cost. HM Digital, Inc. is the only manufacturer of economical in-line dual TDS monitors that measure total dissolved solids (TDS) levels of feed and product water lines simultaneously, an effective way to compare rejection rates and gauge reverse osmosis membrane, water filter and water purification performance.

With HM Digital water testing instruments, you'll know if your water is pure.

Please click products to learn more about which TDS tester is right for you.

What is a TDS meter and what is TDS (Total Dissolved Solids)?

Product Highlight | Upcoming Events

New Product!  Triple Inline TDS Monitor
New Product! Triple Inline TDS Monitor

The TRM-1 is a three sensor TDS monitor that can monitor the TDS levels at three different points. It is perfect for RO/DI combo systems and other types of filtration and purification systems.

Read More ...
Indoor Gardening Expo - San Francisco
Indoor Gardening Expo - San Francisco

The biggest trade show for hydroponics, indoor gardening and greenhouses. San Francisco, California, July 26 - July 27, 2014. Visit us at booth #540.

Read More ...