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.

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.

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.

if you not sure about when to replace your water filter cartridge, one of the best way is just do it every 6 months like manufacture recommended. but with this TDS monitor it's even more accurate and prolong and maximize your RO filter.

J'avais acheter HM Digital Dual TDS Mètre pour contrôler la conductivité de l'eau à l'entrée et la sortie de mon osmoseur je me suis aperçu que les 2 sonde n'indiquer pas la bonne valeur .j'ai acheter une soluiton d'etalonage comme precisé (TDS 342 PPM HM DIGITAL) sonde 1=459ppm et sonde 2=448. en voulant recalibre mon appareille et en suivante les instruction [ Si la lecture sur le moniteur (pour l'une ou l'autre ligne) ne correspond pas à la solution, ajustez la lecture vers le haut ou vers le bas en tournant doucement les équipages en plastique orange à l'arrière de l'appareil dans le sens des aiguilles d'une montre ou dans le sens inverse des aiguilles d'une montre pour augmenter ou réduire la lecture.] je me suis aperçu qu'il n'y a pas les vis de réglages.Ducoup l'appareille ne me sers a rien si je ne peux pas l’étalonner ,j'espere que se commentaire permetra a d'autre personne de ne pas se faire avoir.

I bought this product to replace same one I had problem I had with the last one one of the wires came loose at the back of the price if I had the diagram I would’ve put it back yes I was happy with it but it would’ve been nice if there had been a wire diagram or spare parts to replace.

This TDS meter works great with water filtration systems where you want to regularly monitor the water quality. Installation starts with the mounting bracket which can either be stuck on with double-sided tape or screwed onto a cabinet door like I did. The meter easily slides in and out of the bracket which is necessary for future battery changes.Connection to the RO system is simple - the red line (labelled IN) goes between the cold-water source and the RO filter's input line, while the blue line (OUT) goes between the RO's output line and the RO's faucet. All connections use quick-connects which means no extra hardware needed - just push the tubes into the tees. The manual warns about not pushing too far in which can damage the sensor, so measure and mark the tubes before inserting them.Using the meter is also straightforward; press the power button, a light comes indicating which line it's reading, then a continuously updated reading appears on the LCD display. Pressing either IN or OUT buttons gives readings for that line. The meter remembers which line was last chosen, which is handy because I mostly keep an eye on the quality of my filtered water. The meter automatically shuts off in a few minutes to save on batteries. The dual meters are far more convenient than individually reading samples of tap water and then filtered water with a handheld. This meter is pre-calibrated, but I confirmed its accuracy with a handheld.I installed this alongside a new Watts five-stage RO system and I'm glad it did - it helped me find out that the membrane was defective new out of the box! At first, my unfiltered water averaged between 160-180PPM while filtered water came out around 60-80 - at 66% filtration, that's far below the advertised 92%+. After a membrane replacement under warranty, it now reads around around 3-8PPM which is the same as what the local bottled water store sells.The biggest gripe with this meter is the lack of a battery door - especially where there's room for one. Instead, 4x screws need to be removed to get to the batteries. On that note, it's nice that it uses 2x AA batteries which should be both easy to find around the house and last longer than mini-button cells. A lesser design issue is the bad choice of location for the line IN/OUT LED lights - they're bright and so close to the LCD display, it's distracting - they should have put the LED's behind the display to make it backlit and readable in the evening.Overall, this a must-have for water filtration systems if you want to take the guesswork out of replacing RO membranes and filters. I paid slightly less than the price of two handhelds, but the dual meters in this monitor makes it a convenience that's worth spending the extra money on.

When you get it to turn o. It's a great and quite accurate tds meter. Easy to install. Down side its very hard to turn on often press the power on button more than a dozen times and wriggle it around then it goes on and works great. But is the same hassle everything you want to use it. So should be 5 stars but can only give it one.

I am using the HM Digital DM-2 to measure the input and output of my reverse osmosis system. I have tested accuracy with other instruments and found it accurate and reliable.It's well made and robust. One small comment: the LED light indicator is too bright overwhelming the LED screen. Otherwise it is perfect.