KH Director reading 1dKH low after calibration

[arking_mark]

Recently, I noticed that my KHD measurements were low.

When I checked against my Hanna, KHD was measuring about 1 dkH lower.

I recalibrated the KHD and was still getting a 1dkH difference.

I bought the GHL 7.5dkH reference to see if there really was an issue.

The KHD measured the 7.5dKH reference at 6.5dkH. Also a 1dkH difference.

I assumed the pH probe needed to be replaced and bought a replacement..

After recalibrating with the new probe, it still measured the 7.5dKH reference as 6.5dKH.

When I looked back at my history, it appears this issue may have started in late January.

Please advise.

 

[Lasse]

Some silly questions - Have you checked your filter? Calibrate sample pump and reagent pump?

Do You know that you have a a possibility to adjust here

Sincerely Lasse

 

[reeferisland]

Recently, I noticed that my KHD measurements were low.

When I checked against my Hanna, KHD was measuring about 1 dkH lower.

I recalibrated the KHD and was still getting a 1dkH difference.

I bought the GHL 7.5dkH reference to see if there really was an issue.

The KHD measured the 7.5dKH reference at 6.5dkH. Also a 1dkH difference.

I assumed the pH probe needed to be replaced and bought a replacement..

After recalibrating with the new probe, it still measured the 7.5dKH reference as 6.5dKH.

When I looked back at my history, it appears this issue may have started in late January.

Please advise.

I recently went through what you just did and found out my Khd is +.5 off. I tried the -.5 adjustment and it does not apply it so I aim for a dkh measurement that is .5 higher than I want, which will give me the number I really want.

 

[arking_mark]

Some silly questions - Have you checked your filter? Calibrate sample pump and reagent pump?

Do You know that you have a a possibility to adjust here

Sincerely Lasse

Thanks @Lasse.

I calibrated both pumps and made an offset for the measurement.

However, I'm not understanding why the measurement is off, and would like to correct the underlying problem so I can have confidence in the KHD product.

 

[Lasse]

If the sample pump will give lesser amount - let us say 70 ml instead of 80 ml - the critical pH (in the titration) will be reached earlier - the same if the reagent pump gives to much. dKH is calculated from how much of the reagent is used. Amount of sample is calculated from the running time of the sample pump, reagent amount is calculated from the reagent pumps running time. One of the reason for lesser sample amount is - IME - often that the filter is clogged

if you both have calibrated and done an offset - you probably will get a to high result

Khd is +.5 off. I tried the -.5 adjustment and it does not apply it

If dKH is 7.5 instead of 7 - the 5 % adjustment will only adjust the amount with 0.35 dKH. It is also difficult to compare between different tests - they can have different endpoints in calibration.

Sincerely Lasse

 

[arking_mark]

@Lasse
I will replace the filter and see what happens.

However, I expect that any flow restriction from the filter would be reflected in the sample pump flow rate.

 

[Lasse]

However, I expect that any flow restriction from the filter would be reflected in the sample pump flow rate

Yea - it will be but I have had variation in flow rate when larger particles been sucked up in the filter. hence jumps in detected dKH

Sincerely Lasse

 

[arking_mark]

Yea - it will be but I have had variation in flow rate when larger particles been sucked up in the filter. hence jumps in detected dKH

Sincerely Lasse

Flow rate went from 34 to 32.5...I had expected it to go up. I measure 3 times.

 

[Lasse]

Flow rate went from 34 to 32.5...I had expected it to go up. I measure 3 times.

Why expected it to go up? The first 34 ml/ minut will mean that the pimp have to run 80/34 minute to get 80 ml -> 2,35 minutes. In reality - with 32.5 ml/min - it give you a sample value of 2,35*32,5 = 76,4 ml - this can explain some of the reasons why you get to low measurements. Do you use a scale and your saltwater when you calibrate. In these case - I normally divide the weight I get with 1.024 in order to get the right volume of saltwater. Density 1.024 - PSU around 35

If my calibration sample give me a weight of 30 g -> 30/1.024 = 29,3 ml. But it is difficult to know the density of the reagent - therefore i may be better to always use RO water as calibration fluid - 1 g will be 1 ml in this way. @Vinny@GHLUSA What do you recommend for calibration fluid infor weight calibration with KH and Ion directors? RO or the fluid you actually use?

Sincerely Lasse

 

[arking_mark]

Why expected it to go up? The first 34 ml/ minut will mean that the pimp have to run 80/34 minute to get 80 ml -> 2,35 minutes. In reality - with 32.5 ml/min - it give you a sample value of 2,35*32,5 = 76,4 ml - this can explain some of the reasons why you get to low measurements. Do you use a scale and your saltwater when you calibrate. In these case - I normally divide the weight I get with 1.024 in order to get the right volume of saltwater. Density 1.024 - PSU around 35

If my calibration sample give me a weight of 30 g -> 30/1.024 = 29,3 ml. But it is difficult to know the density of the reagent - therefore i may be better to always use RO water as calibration fluid - 1 g will be 1 ml in this way. @Vinny@GHLUSA What do you recommend for calibration fluid infor weight calibration with KH and Ion directors? RO or the fluid you actually use?

Sincerely Lasse

Interestingly enough, I use weight for my Maxi dosers and graduated cylinders for my KHD.

 

[arking_mark]

So no real change in measurement. Maybe 0.7dKH low vs 1dKH low. I'll let it run several more times before testing against the GHL 7.5dKH reference.

 

[arking_mark]

Why expected it to go up? The first 34 ml/ minut will mean that the pimp have to run 80/34 minute to get 80 ml -> 2,35 minutes. In reality - with 32.5 ml/min - it give you a sample value of 2,35*32,5 = 76,4 ml - this can explain some of the reasons why you get to low measurements. Do you use a scale and your saltwater when you calibrate. In these case - I normally divide the weight I get with 1.024 in order to get the right volume of saltwater. Density 1.024 - PSU around 35

If my calibration sample give me a weight of 30 g -> 30/1.024 = 29,3 ml. But it is difficult to know the density of the reagent - therefore i may be better to always use RO water as calibration fluid - 1 g will be 1 ml in this way. @Vinny@GHLUSA What do you recommend for calibration fluid infor weight calibration with KH and Ion directors? RO or the fluid you actually use?

Sincerely Lasse

The rate of the sample pump was higher with the old filter. Assuming the old filter was clogged, one would expect a slower rate.

 

[Lasse]

The rate of the sample pump was higher with the old filter. Assuming the old filter was clogged, one would expect a slower rate.

I got it

Sincerely Lasse

 

[arking_mark]

After 3 separate pump calibrations....my KHD still reads the GHL 7.5dkH reference as 6.5dKH. Grrrr....

 

[arking_mark]

I guess I could recalibrate the pH probe again...

 

[Vinny@GHLUSA Verified Sponsor]

@Lasse
I calibrate with the liquids that are being dispensed by the dosing pump. The weight difference between RO and SW in small samples are minimal. That's where the adjustment tool comes in. As long as the device consistency is there, one can use it to adjust for these differences.

@arking_mark
After you calibrate the probe, if the numbers are still a consistent 6.5dkH even with a brand new filter, set the adjustment to +15%. Keep in mind the tolerance when using the KHD (+/- 0.2) and Reference fluid (+/- 0.2) is +/- 0.4dkH.

 

[gbroadbridge]

After 3 separate pump calibrations....my KHD still reads the GHL 7.5dkH reference as 6.5dKH. Grrrr....

Did you try another bottle of reagent?

 

[arking_mark]

Did you try another bottle of reagent?

Good call.

I'm almost done with this one and will need to swap soon. However, I don't thinks these reagents really deteriorate.

 

[gbroadbridge]

Good call.

I'm almost done with this one and will need to swap soon. However, I don't thinks these reagents really deteriorate.

Well, the reagent is, I believe, simply 0.02N HCl plus a drop of pretty blue colouring.

If there is evaporation to make it more concentrated it will read low Alk. It would only take a few ml evaporation.

Of it could have been simply slightly out to start with ...

Just a guess

 

[Mandarin64]

Good call.

I'm almost done with this one and will need to swap soon. However, I don't thinks these reagents really deteriorate.

Hi

Did you sort out your issue as I have exactly the same problem, under reading by 1.2 dkh with the 7.5 dkh reference fluid ?
Also using an adjustment of 17% only gives 6.8 dkh.

regards

Steve