I decided to buy a TDS meter about two weeks ago to see if I needed to replace my filters since it had been a long time since I had done so. I checked my TDS and as suspected it was much to high for my likings at 65ppm, so I replaced all my cartridges and membrane on my 4 stage RODI unit. After changing all the cartridges I checked my new water and it had a TDS of 2ppm. I was very happy with the results, but what's strange is I've tested each new batch of water since then and the TDS has continued to climb up. My fresh water is now reading 45ppm and I dont understand it. Could anyone shed some light on this? It's only been two weeks since I got the 2ppm reading. It's a HM digital TDS meter that I got from the LFS.
TDS meter and its readings advice
- Thread starter ksicard
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You may want to purchase the following item:
HM Digital C342 TDS and EC Calibration Solution, 342 ppm (NaCl), 90 ml Volume .
I'm not sure what model TDS you purchased, but my research had me purchase this product. Some people recommend buying the 1000 ppm calibration solution, but I purchased the 342 ppm solution because my end result that I want is 0 ppm on my RO/DI water.
Wannabee
How much water have you run through the membrane? Membranes have a preservative on them that needs to be flushed away by running water and discarding it.
Also, yes, let it run for a bit before testing it and catch the water right out of the output line if you're using a hand-held meter, if it's caught in a container that can affect the TDS. (Ie particles in the container etc.)
What's the TDS if your incoming (unfiltered) water?
Also, yes, let it run for a bit before testing it and catch the water right out of the output line if you're using a hand-held meter, if it's caught in a container that can affect the TDS. (Ie particles in the container etc.)
What's the TDS if your incoming (unfiltered) water?
Okay I def think it might be the container that the water is in. I did what was suggested and tried catching the water in a diff container and testing it and got a reading of 145ppm. In order to get an accurate reading what kind of container should I use to test the water? I tried two different containers and got two different readings so I think it's def related to the container.
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When any RO system first starts up, you'll get a pulse of not-so-clean water coming out of it. This is due to a process called "TDS creep." We can talk more about why this happens if you're interested, but bottom line, let the system run for a full 2 minutes before you sample the water for purposes of a TDS reading. Here a graph of how the TDS readings change over the first couple of minutes from a system we tested that had a 75 gpd membrane.
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We measure Total Dissolved Solids in parts per million, or "ppm." We often try to measure TDS down near 0 ppm. Because this TDS level is so low, we have to keep in mind the sensitivity of the meter used to measure it, and the technique used to measure the tds.
Nearly ANY contamination in the sample container will cause an erroneous TDS measurement. Some plastic containers are difficult to get absolutely clean, and although they appear clean, they are not. An easy standard approach is to use a drinking glass as a sample container - use one right out of the dishwasher. Obviously, keep your fingers away from the inside surface of the glass.
Calibrate your meter. Use a calibration fluid generally in the range of the tds measurements you'll be taking. Some meters require a specific tds calibration fluid (e.g., 800 ppm), regardless of the tds levels in your samples.
Be careful with how you take your samples. Let's say you intend to measure the TDS in your 1) DI water, 2) RO water, and 3) tap water. Start with the cleanest of the three - the DI water. After letting the system run for a sufficient period of time that you are sure the tds levels have stabilized (to assure you are not measuring tds creep water), rinse the sample container two or three times with the water you intend to sample, and then fill the sample container with sufficient DI water to take a reading.
Now on to the RO water. The water we are interested in here is the permeate – i.e., the water that has been purified by the RO membrane – not the waste water. Make sure you understand which is which before taking the sample. You may need to unhook some tubing – likely where the tubing attaches to the “in” port on the DI housing in order to take this sample. This is inconvenient for many people, and we find that people never do it. They report only the tap water TDS and the DI water TDS. Contact Buckeye if you need guidance regarding installing a couple of extra fittings and tubing to facilitate measuring the TDS of the RO water (permeate). When you take the sample, follow the same procedure described above – use a clean sample container, assure you are not measuring TDS creep water, rinse with the permeate several times before taking the sample, and use a calibrated meter.
Use the same approach to collect and measure your tap water as well.
Russ
We measure Total Dissolved Solids in parts per million, or "ppm." We often try to measure TDS down near 0 ppm. Because this TDS level is so low, we have to keep in mind the sensitivity of the meter used to measure it, and the technique used to measure the tds.
Nearly ANY contamination in the sample container will cause an erroneous TDS measurement. Some plastic containers are difficult to get absolutely clean, and although they appear clean, they are not. An easy standard approach is to use a drinking glass as a sample container - use one right out of the dishwasher. Obviously, keep your fingers away from the inside surface of the glass.
Calibrate your meter. Use a calibration fluid generally in the range of the tds measurements you'll be taking. Some meters require a specific tds calibration fluid (e.g., 800 ppm), regardless of the tds levels in your samples.
Be careful with how you take your samples. Let's say you intend to measure the TDS in your 1) DI water, 2) RO water, and 3) tap water. Start with the cleanest of the three - the DI water. After letting the system run for a sufficient period of time that you are sure the tds levels have stabilized (to assure you are not measuring tds creep water), rinse the sample container two or three times with the water you intend to sample, and then fill the sample container with sufficient DI water to take a reading.
Now on to the RO water. The water we are interested in here is the permeate – i.e., the water that has been purified by the RO membrane – not the waste water. Make sure you understand which is which before taking the sample. You may need to unhook some tubing – likely where the tubing attaches to the “in” port on the DI housing in order to take this sample. This is inconvenient for many people, and we find that people never do it. They report only the tap water TDS and the DI water TDS. Contact Buckeye if you need guidance regarding installing a couple of extra fittings and tubing to facilitate measuring the TDS of the RO water (permeate). When you take the sample, follow the same procedure described above – use a clean sample container, assure you are not measuring TDS creep water, rinse with the permeate several times before taking the sample, and use a calibrated meter.
Use the same approach to collect and measure your tap water as well.
Russ
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That will sure do it! Hope you didn't eat up too much of your DI resin capacity in the process.
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I'd use the color change as only a rough gauge - think of it as a prompt that you have to break out your tds meter and start paying closer attention to your DI water TDS. Sometimes you can get months out of a DI cart after it starts to change color, other times you get much less.
Russ
Russ
