Commercial In-Line Dual TDS Monitor

I have used a GE Reverse Osmosis (RO) water purification system for nearly 10 years. I have been using a single portable total dissolved solids (TDS) meter to check my water and I have had very little need for this more sophisticated device until things started to go wrong due to the age of the RO system. I started seeing poorer quality water, and thought I needed a set of new filters (RO filter, pre and post filters). It turned out that I needed a new shut-off valve, but on the way to this conclusion I installed one of these DM-2 meters. I now have two of them. Each meter has two probes to measure TDS. I installed two probes on the input and output of the post-filter, and two probes on the input and output of the pre-filter. This arrangement allows the two input probes to measure the TDS before and after the RO filter, and the two output probles to measure the performance of the pre- and post-filters.I have checked the calibration of the DM-2 instrument using a standard sodium chloride solution and it was accurate as shipped to me. The meter and its probes are reliable and stable measurement devices. They use the electrical conductivity of the water to estimate the TDS of the water. My purified water comes out to be in the 3-10 parts per million (ppm) range, and my input is softened well water and comes out to be around 145 ppm. For 5 ppm RO water, this is ((145-5)/145)*100% or 96% RO filter efficiency. This efficiency varies with the type of RO filter in use.When you use this device, its important to understand exactly what you are measuring. It turns out that the output of the RO filter is pretty reliable and stable, but a new post-filter tends to pollute the water with preservatives and other particles that I know nothing about. Hence, measuring TDS at the output of the post-filter might make you think the RO filter is not working. However, as the filter washes through over a couple of days, the TDS will improve. All the while, the TDS from the RO filter itself is usually just fine right from installing the RO filter.These instruments come standard with 1/4" quicklock plastic "T" fittings, which allow the probes to penetrate right into the middle of the water stream. Some of my water lines are 3/8" so I used 3/8" "T" fittings which I purchased separately. As these fittings are a bit bigger than the 1/4" fittings only the probe tips stick into the water stream. This caused me no problems at all, with identical measurements within the variability in TDS of my water. I did try putting 1/4" fittings in my 3/8" lines by use of couplings and so on, but this was a lot of trouble and gave identical readings to the 3/8" "T" fittings.Conductivity technology is really well-established, gives reliable results, and these meters do a good job of implementing the technology in RO water purification systems. Its really convenient to have a permanently mounted measurement arrangement to monitor performance. The meter will work with any RO system, not just the one I have been using. I recommend installing these right from the start.

My old handheld TDS meter since I installed my RO system retired after some 18 years. (Yes, my kid went to college.) I had an eye for these inline systems for a long time. It's not necessary but you don't need to rinse the meter with enough input or output water to avoid cross contamination. This guy has two electrodes and they are ready whenever you want to take readings.I got a brand new looking meter. The electrodes are solid stainless steel embedded in solid plastic. The T connectors are John Guess, the same as all my connectors in my system. The electrodes are of the correct size so there is no leak. I don't even want to mount the meter. When I need to take a reading, I just turn on the power button, read the current display, and press the button for the other reading. So convenient.

There is no way to calibrate this meter, and the meter I was sent is at least 100 ppm out of calibration when measuring the calibration buffer. The online product information indicates that there is a calibration screw that can be adjusted. There is no such screw on this model, I don’t believe the unit can be calibrated by the user. So far the seller cannot provide a fix. I cannot recommend this meter.

Best TDS Monitor I have ever used. I compared the reading to another high quality accurate hand-operated unit and they both registered the same results. This is better than I expected from reading the reviews. Love the illuminated display so easy to read in the dark or low light.

This thing works great. Bought it for my brothers home-made RO water tank set up for washing cars. To get spot free water you need it to have it in the teens or lower in ppm and this thing allows us to know when its time to replace the membranes. Would recommend to anyone.

Ppm is way off. Have several others that all read +/-1 and that are all adjustable. I have calibration solution. Brand new. Reads +153 off from the 342 ppm calibration solution.

I used it for 3 weeks before realizing that is was approx 220 ppm off from factory. After adjusting, the incoming probe gave out a week later. The outgoing probe is still working. Once calibrated, it is very fast in reading the ppm. Just wish that i had two instead on one probe.

Larger, sturdier, longer leads, and this one can actually be calibrated. Only issue is a "commercial" version should come with 1/2" tee, as most commercial RO's don't use 1/4" tubing.