COM-100 TDS Meter Question

[Buckeye Hydro]

Ah-ha. That's a little different, but not much. That's the functional equivalent of the Axeon HF4 4040.

That membrane is spec'ed at 100 psi @ 99% rejection @ 15% recovery. 40 psi feedwater going through a 10"x2.5" carbon block and sediment filter still "ain't gonna cut it."

 

[Randy Holmes-Farley]

He is way under the minimum prescribed concentrate flow for a 4" element - he doesn't have enough water flowing through the membrane to adequately flush out what doesn't pass through the membrane.

OK, so we'd expect that with an added pump, he'll get less efficiency in terms of water used to water produced, but will get more water and a lower TDS of the product water?

 

[Buckeye Hydro]

Probably - he's at 50% recovery now, with insufficient feedwater and concentrate. But especially if we add concentrate recirculation to his system I suspect we could keep him at ~50%. He have very high quality feedwater based on the little bit of info I have so far.

 

[gdemos]

My meter reads tap water at approx 70ppm NaCl. I make approx 200g RODI monthly and replace my sediment, carbon, and DI 10" about every 10 weeks by then my inline tds DI reads 2ppm with RO at maybe 6ppm after running a while. I went for the super size membrane mostly for speed of production and now finding I'd like to run it a bit more like the way it is intended.

 

[Forsaken77]

I have the Com-100 also and it has to be calibrated. Amazon sells their 342 calibration solution. None of these meters come properly calibrated from the factory. Also, you have to hold the meter in the sample a good 2 mins for the temp to accurately display. I dip mine right in the RO/DI trash can that has a thermometer, heater and circulation pump. So it takes a bit for the temp on the COM-100 to reach that of the thermometer.

 

[Randy Holmes-Farley]

I have the Com-100 also and it has to be calibrated. Amazon sells their 342 calibration solution. None of these meters come properly calibrated from the factory. Also, you have to hold the meter in the sample a good 2 mins for the temp to accurately display. I dip mine right in the RO/DI trash can that has a thermometer, heater and circulation pump. So it takes a bit for the temp on the COM-100 to reach that of the thermometer.

How far off was it when it arrived?

 

[Forsaken77]

How far off was it when it arrived?

I believe it was telling me out of the box I had zero tds on NaCl, which I knew was off because I had used up filters and bypassed the DI. After calibration it showed roughly 2.5 tds. I started with their cheap brown one and never got the same result twice with the calibration fluid. Then I got the COM-100 and it was a decent amount off out of the box. That's why I always recommend calibrating these meters first, just like you would any digital aquarium equipment. It may not have been exactly 2.5, but it was out of range enough to make a significant difference.

 

[volivier]

I have the com 100 also, and have no idea what to set it on, or what to buy for calibration. It has .5 or .7 options for ppm. I have an inline tds meter, but got the com 100 to double check the zero reading from my ro/di filter.

 

[Buckeye Hydro]

I have the com 100 also, and have no idea what to set it on, or what to buy for calibration. It has .5 or .7 options for ppm. I have an inline tds meter, but got the com 100 to double check the zero reading from my ro/di filter.

We've been an HM Digital Distributor since the bronze age. Unless you have reason to do otherwise, select the NaCl scale. We have 342 ppm calibration solution.

 

[volivier]

When I turn the meter on the modes it shows the u$, m$, ppm 07 and .5, ppt .7 and .5

We've been an HM Digital Distributor since the bronze age. Unless you have reason to do otherwise, select the NaCl scale. We have 342 ppm calibration solution.

 

[lvzx14]

I'm in the same boat, picked one up a couple weeks back but haven't had a lot of time to mess with it yet.

Just started reading the manual so I will be following this topic

 

[Buckeye Hydro]

Volivier - pm me your email address with a request and I can send you the product manual.

Russ

 

[volivier]

I have the manual, it seems mine doesn't show the same options as what the manual says. I don't have kcl or nacl on mine.

 

[Buckeye Hydro]

Which conversion scale would you like to select? The NaCl scale?

 

[Randy Holmes-Farley]

I discuss what the different units of measure (442, NaCl, etc. ) mean here:

What is TDS? by Randy Holmes-Farley - Reefkeeping.com
http://www.reefkeeping.com/issues/2004-04/rhf/feature/index.htm

from it:

True TDS meters (that only give output in TDS units, such as the Oakton TDS Tester shown in Figure 4) typically convert the conductivity reading into the ppm concentration of some salt that would give the same measured conductivity. For example, it might be set to give as its output the concentration of sodium chloride (NaCl) that would give that same conductivity. So if the device detected 447 mS/cm, it might display that as 215.5 ppm, as that is the concentration of sodium chloride that gives that same conductivity.

Unfortunately, there is no single exact conversion between conductivity and ppm NaCl as the conductivity of a sodium chloride solution is not linear with concentration (that is, 20 ppm NaCl is slightly less conductive than twice that of 10 ppm NaCl, the reasons for which are beyond this article, but in a sense, the more ions there are in solution, the more they interfere with each other in terms of sensing the voltage, and in terms of moving in response to it). Nevertheless, for values in the range sensed by most TDS meters, a rough conversion is that 1 ppm NaCl = 2.1 mS/cm.

Now the fun really begins. The problem with such devices, at least when not carefully calibrated, is that it is not clear whether it is referring to ppm of sodium chloride equivalents, or to something else. Potassium chloride (KCl) is actually used as the standard more often than sodium chloride. Additionally, researchers often use something called 442, which is a mixture of sodium sulfate (40%), sodium bicarbonate (40%) and sodium chloride (20%). The 442 mixture is designed to mimic the ions often present in natural fresh water systems.

These systems all have slightly different relationships between concentration (in ppm) and conductivity (in mS/cm). Table 2 shows this relationship for some commercial conductivity standards made by Oakton. For many aquarium purposes, it may make little difference whether the true value corresponds to 10 ppm NaCl or 10 ppm 442, but there is a 30-70% difference in the measured conductivity and hence in the total ions present. Consequently, two aquarists using different meters (which may use different standards) may get substantially different results on the same water. Of course, if you calibrate the meter yourself (if that is possible, not all meters can be calibrated), instead of accepting a factory calibration, then you eliminate this concern since you know exactly what you calibrated with.

 

[Buckeye Hydro]

If you're not sure which scale to use, realize that if you weren't given the choice - as is the case with the vast majority of TDS meters in this price range, they would likely use the NaCl scale. Randy - is this your experience?

Russ

 

[Buckeye Hydro]

The conversion factor of "0.5" is the NaCl conversion factor on the COM 100

 

[Randy Holmes-Farley]

If you're not sure which scale to use, realize that if you weren't given the choice - as is the case with the vast majority of TDS meters in this price range, they would likely use the NaCl scale. Randy - is this your experience?

Russ

I've not really checked many to know, but in the absence of any other information, I'd assume it is ppm NaCl calibration.