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Two TDS Pens Reading Differently


Duff0712
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So I have access to two TDS pens. Mine and one at work. Both are the HM Digital TDS-3 Pen. Mine is reading at 50+ TDS higher than the one from work. I have no idea if mine is wrong or my work's is wrong, or both are wrong. I tried them both on my RODI and Distilled water from the store and both are reading 0...

 

I don't have access to calibration fluids right now, is there anything else I can do?

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You could test both in RODI water and see which one is closer to 0 TD. Distilled water at the grocery store can be another alternative if you dont have RODI.

 

I will try them both in Distilled again. Depending on which TDS meter is off, I am afraid if it is mine then my RODI water is off. It's been awhile since I exchanged the inside media, but I hadn't really used it until the last couple months.

 

To testing!

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So I tested both of them in distilled water from the store. One read 0ppm, mine read 1ppm. Would that be enough to give a 50+ppm difference in tank water? I tested them in several different tanks.

Does your pen compensate for temps? Dont know if that would make a difference.

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Does your pen compensate for temps? Dont know if that would make a difference.

 

I don't believe it does. It does have a separate mode for temperature reading, but I rarely used it. 

 

My TDS pen does have a hole in the back for adjustment. I just dont have any TDS specific fluids to test with or know whats going on lol.

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A quick check on the HM Digital site says they calibrate their pens with a 342ppm NaCl solution. I think I am going to buy that just to make sure. I also remember that I decided to stick it into my saltwater tank a month ago. That might have messed it up pretty good. It took a hour before it would do any readings again.

 

 Any ideas of things I can do/test in the meantime?

 

edit:

Thought I'd share what I found

 

"HM Digital meters come factory calibrated (at 342 PPM or 1413 µS, depending on the product) and are ready to use out of the box. They are designed to stay consistent. However, after prolonged usage, it may help to recalibrate your meter using a commercial standard NaCl-based solution (for most HM Digital meters), which is approximately, 0.5 µS of conductivity."

 

Thinking about it now I think I either messed up the calibration of my pen, or my pen is just going bad. I think for now I will take an average reading of my pen and my works pen for a reference and buy the solution and a new pen to be on the safe side.

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I use use 342ppm NaCl solution to calibrate.

I'm going to do that to be on the safe side. My tanks GH and PH seem to be fine so I'm not too worried. Just dont want my TDS to go out of control haha. My pen has been saying its increasing by like 10 a day. My wastes haven't been changing and don't know if y pen is like multiplying only like a couple TDS to 10.

I just want it fixed lol

I have another edit:

So I am pretty sure I know why my TDS has been increasing the past few days. Not only is it probably a bit of leaching from the cholla, but adding in the prime I've found is probably the cause. Solved one thing haha. Thought I'd share.

-Duffy

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I'm going to do that to be on the safe side. My tanks GH and PH seem to be fine so I'm not too worried. Just dont want my TDS to go out of control haha. My pen has been saying its increasing by like 10 a day. My wastes haven't been changing and don't know if y pen is like multiplying only like a couple TDS to 10.

I just want it fixed lol

I have another edit:

So I am pretty sure I know why my TDS has been increasing the past few days. Not only is it probably a bit of leaching from the cholla, but adding in the prime I've found is probably the cause. Solved one thing haha. Thought I'd share.

-Duffy

Prime will do that.

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A bit of an update for anyone following this. I got my calibration solution in today (TDS Pen should arrive tomorrow), so I figured I would test out my current Pen.

 

The solution is a TDS of 342ppm. So assuming the solution is correct, these are my results.

 

TDS Before Calibration:

Tank - 185ppm

Calibration fluid: 410ppm

 

TDS After Calibration:

Tank - 156ppm

 

So my pen was OFF. I will test the new TDS PEN (HM-Digital TDS-EZ) tomorrow in the calibration solution first to see if it does in fact come pre calibrated then test it with my current pen as well.

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I didnt know you had ro calibrate TDS pens?

Yea most need it eventually, it's almost easier to buy new ones as they are pretty cheap. Don't beat yourself up though trying to figure it out. Go with the lower number and buy one once a year

Sent from my SM-G900V using Tapatalk

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TDS pen arrived today. Figured I'd do some tests. The blue one is the new one.

Right out of box testing both in tank

13167284969c8428e2b0272b877b622f.jpg

Testing the new pen in the 342TDS liquid.

3f06dc7e07026998af8b51916466520b.jpg

Retesting my old pen I recalibrated yesterday.

82b60fb48c621a83d6b8be7fcf6c8295.jpg

What do you guys think?

-Duffy

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Both need to be recalibrated, older pen is closer. Now that you have the solution you can check pens.

 

I always wondered why the solution is 342ppm?

 

Weird that the new pen needs to be recalibrated... Oh wells. Glad I got the solution :)

 

Seems weird to me to that it is 342ppm. I'm sure it has to do with something chemistry related.

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Ave. tap water is about 350ppm, that's why a 342ppm solution is used.

Using the meter in your salt tank probably affected calibration.

If your meter is not temp. compensated, the accuracy does vary about 2-4% for every degree C above/below 25C.

Plus I think HM says accuracy is within about 2%, without factoring in temp differences.

Those HM calibration solutions have a 6mo shelf life after opening; write the date on the bottle :) And remember to always put a dry pen in there, so you don't contaminate them.

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Why can't ro water be used to calibrate the pens?

I would say it's due to the fact that you want it well calibrated at the kind of usage you've got.

Instruments measurement aren't always perfectly linear. When you calibrate at 0 ppm, you are at an extreme value on the range so it might not be as precise for higher value.

Envoyé de mon SGH-I337M en utilisant Tapatalk

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