TDS meters are great for letting you know how clean your RODI water is. TDS stands for “Total Dissolved Solids” and is basically a conductivity meter that measures the resistance of the water that you are testing. TDS can be a multitude of things from calcium, magnesium, or anything else that has an electrical charge in your water. On a RODI system, we suggest using an inline style TDS meter that plugs inline with your systems plumbing, giving a much more stable reading. Inline TDS probes can be installed in a variety of locations throughout a RODI system letting you know what kind of quality water your house has, RO membrane is producing, and your DI system.

  1. Turn the source water off and relieve any pressure in your RODI units lines. 
  2. Determine the location that you want to install your probe. Certain models come with multiple probes that can be fitted in different places throughout your RODI system. Please see below for suggested locations.
  3. Cut the RO tubing where you wish to install the metering probes and install the push connect “T” fitting so that water flows through the straight side of the fitting.
  4. Push the probe into the “T” fitting so that the metering tips are perpendicular to the flow of water for the best results.
  5. Once the probe is installed slowly turn your source water back on and check for any leaks around the fittings.

Suggested Metering Locations:

Directly out of your tap – The TDS of your source water is important to know how efficient your RO membrane is running. In most cases, this will range from anywhere from 50 to 400+ depending on your particular water source.

After your Membrane/Before DI – Your membrane should be removing a majority of the TDS from your source water. Depending on what is in your water membranes can remove up to 99% of contaminants from tap water. The TDS of the water coming out of your membrane will also be the amount of TDS that your Deionization Resin will need to remove.

Between DI Canisters – If you have multiple deionization canisters, it is worthwhile to know how much TDS is being removed by the first DI cartridge, and how much is required to be removed by any secondary DI canisters.

After your DI – After your deionization canister is the final product water that you will be using. For reef tanks, we suggest keeping the final reading on your TDS meter at zero. This reading is the most important location to know the TDS.







If you have any other questions or need further help contact our reefing experts at 763-432-9691.