Anyone know how to recalibrate a tds meter?

[Tony40]

Been using r/o d/i water for years never had a tds meter just changed sedimate,carbon,d/i filters every 6 months and r/o membrane every year now that i seen the podcast of the r/od/i went and ordered a tds meter and to my suprise have a reading of 13 with new everything my water here from the supply in vegas is terrible a 341 on the in moved the meter around and have it hooked up after the sedimate and carbon,and r/o membrane and get a reading of 19-21 then after the d/i chamber it comes out at 12-14 most of the time a 13 after watching the podcast tell me to change all filters at 10tds could it be my filters are not good enough or could this meter be wrong really would like to know if anyone has recaliprated one

[CarmieJo]

When did you last change your filters?

[Phurst]

I've never seen a TDS meter that can be calibrated. I'd suspect the water really does have a TDS reading that high. I too am interested in when your meters were last changed. 341 is REALLY high. You might consider using a dual DI stage just to keep those numbers down.

[rroselavy]

Many TDS meters (like the one I just bought) can be calibrated with a mini screwdriver and some reference solution (typically 342 ppm and 1000 ppm solutions). Mine came factory calibrated, but it will be nice to check it someday when things seem out of whack.

If your DI stage is mounted horizontally,make sure to give it a shake now and then to help prevent water channeling through the resin.

Also, flushing your RODI system every once in a while is a good thing. Mine came with a flush valve, but you may have to add that to yours.

I've read that if your incoming TDS is pretty bad, that you may not obtain 0 on the back end. If so, perhaps you should consider a second DI stage.

[Phurst]

Cool, learn something every day

[Tony40]

just ordered some 1000 tds calibration fluid from e-bay for $11 shipped not bad now i will know one way or the other my reading now after 25 gals is 8ppm guess its getting better at any rate

[Tony40]

if anyone intrested in checking their metersCalibration Instructions for HM Digital TDS3 & TDS4 Testers

HM Digital meters are factory calibrated at 342ppm NaCL and are designed to stay consistent. - However, you may need to recalibrate your meter from time to time or for certain applications. TDS meters are most accurate when calibrated as close as possible to the sample being tested. For best results, calibrate at 25 oC (77 oF)

To insure accuracy and consistency, recalibrate your meter using a commercial standard solution. This can be done prior to usage and should be done after prolonged usage.

For drinking water we recommend calibrating in a range of 90ppm to 700ppm.

Make sure your meter is clean and dry before placing it in the bottle of calibration solution so you do not contaminate the solution.

Step 1: Turn the meter on, insert the meter into the calibration solution and read the TDS level of the solution.

Step 2: If the meter does not read within 2% of the solution, adjust the reading by inserting a mini screwdriver into the trimmer pot (small hole on the rear of the meter). Gently turn the trimmer screw clockwise to increase the reading and counterclockwise to decrease the reading.
- Make sure the screwdriver fits evenly into the groove of the screw.
- Note that the trimmer pot is very sensitive! Remove the screwdriver carefully.
- Try to keep the meter vertical.

Step 3: Once the meter reads within 2% of the solution, gently release pressure on the screwdriver and remove from the trimmer pot.
- If the screwdriver is retracted abruptly, the reading may jump.

Step 4: With the meter in the solution and the reading at the correct level, press the "HOLD" button. Let the reading hold for approximately 10 seconds to fully stabilize.

Step 5: Remove the meter from the solution. Shake the meter to remove any water drops that may adhere to the probes and casing, creating air gaps.
- Water droplets or air gaps may cause the meter to display an incorrect reading.

Step 6: Turn the meter off, wait a moment and turn the meter on again.

Step 7: Insert the meter into the calibration solution and verify the reading. If the reading is accurate, calibration is complete. If not, repeat the procedure.

Solution Conversions

342 NaCl =
362 as KCl 478 as "442" 700 µS

--------------------------------------------------------------------------------

1000 NaCl =
1060 as KCl 1450 as "442" 2000 µS

[BuckeyeFieldSupply]

I question the advice to change all filters when your DI TDS level is 10 ppm. Here's a different approach:

A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the useable life of these two filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. This is your indication one or both of the filters is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. The Matrikx+1 (“Chlorine Guzzler”) for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. Original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons.

Regarding your RO membrane and DI resin, use your TDS meter to measure, record, and track the TDS (expressed in parts per million) in three places:
1. Tap water
2. After the RO but before the DI
3. After the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 parts per million (ppm). Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block filter (collectively called prefilters) do very little to remove dissolved solids. So with your tap water at 400 ppm, you can measure the water at the “in” port on your RO housing and you'll see its still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce less purified water (aka “permeate”), but have a higher rejection rate (96 to 98%). The life span of a RO membrane is dependant upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the total dissolved solids (TDS) in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce less water as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the 40 ppm water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm to 3 ppm, 5 ppm, and higher, you know that your resin needs to be replaced. Sometimes people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty” water. This will exhaust the resin quicker then would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!

Russ

[BuckeyeFieldSupply]

I've never seen a TDS meter that can be calibrated. I'd suspect the water really does have a TDS reading that high. I too am interested in when your meters were last changed. 341 is REALLY high. You might consider using a dual DI stage just to keep those numbers down.

Nearly all TDS meters, expect I suspect some really low cost import meters, can be calibrated.

when you consider tds levels across the county, 341 ppm is only a bit higher than average.

The key to removing most of the dissolved solids is a good RO membrane - run at an appropriate pressure. Remember that the DI stage(s) is just a polisher.

Russ

[BuckeyeFieldSupply]

If your DI stage is mounted horizontally,make sure to give it a shake now and then to help prevent water channeling through the resin.[/quote]

Horizontal DI stages are a fundamental design error typically made by vendors who retrofit drinking water systems that are assembled overseas.

If you have a horizontal DI stage, unclip it and orient it vertically with bottom -up flow. Make sure the housing is packed very tightly/completely full with DI resin.

Russ

[BuckeyeFieldSupply]

just ordered some 1000 tds calibration fluid from e-bay for $11 shipped not bad now i will know one way or the other my reading now after 25 gals is 8ppm guess its getting better at any rate

It is best to use a calibration fluid that is close to the numbers you typically measure. We carry for instance 342 ppm, 800 ppm, and 1382 ppm calibration solutions.

Some meters can only be calibrated using a certain ppm fluid.

[BuckeyeFieldSupply]

my reading now after 25 gals is 8ppm guess its getting better at any rate

At 8 ppm from your DI you are long overdue for new DI resin.

We really need three readings to troubleshoot your system

Tap: you reported 341 ppm
RO water:
DI water: you reported 8 ppm

What is your RO water reading? If we know that we can calculate the rejection rate of your membrane.

Russ

[CarmieJo]

Hello Russ and to TR.
Thanks for this valuable contribution!