KHD value high - tried known fixes

[r21]

I've recently setup a KH Director and it is still reporting high dKH. Reports around 2-3 dKH higher than actual value. Here is what I have tried, some of it several times

1. Measured and remeasured all the lines
2. Calculated volume by disconnecting and dispensing into a 50ml graduated cylinder - twice - this was within 2ml of measured/ calculated volume by length
3. Re-calibrated pH probe 3 times - all readings after calibration have been within .2 of 4 and 7
4. Re-calibrated dosing heads twice - each calibration within 0.5ml of each other
5. Checked for air bubbles, multiple flushing and venting reagent
6. I ordered some GHL KH reference fluid and its ran three times 10.2, 10.1, 10 and 10.5 - so very consistent just 2.5 - 3dKH over the reference fluid that its testing
7. For tank water Hanna checker gives me a dKH of 8 and KHD gives me a consistent 10 - 10.3

Saltwater is Tropic Marin Pro made up to std strength i.e. 1kg/30litres which should be about 7-8 dKH which is roughly what Hanna checker is saying

I really don't know what else to check, the only thing which is odd is the waste is being reported much higher than is being produced - waste on dosing pump 3 is showing as 1439ml in the container at most its 950ml - this has been consistently high

I've posted this on GHL's forum too but bigger audience on here, hopefully someone can explain why I'm getting a consistent high reading

 

[Henryb9]

I've recently setup a KH Director and it is still reporting high dKH. Reports around 2-3 dKH higher than actual value. Here is what I have tried, some of it several times

1. Measured and remeasured all the lines
2. Calculated volume by disconnecting and dispensing into a 50ml graduated cylinder - twice - this was within 2ml of measured/ calculated volume by length
3. Re-calibrated pH probe 3 times - all readings after calibration have been within .2 of 4 and 7
4. Re-calibrated dosing heads twice - each calibration within 0.5ml of each other
5. Checked for air bubbles, multiple flushing and venting reagent
6. I ordered some GHL KH reference fluid and its ran three times 10.2, 10.1, 10 and 10.5 - so very consistent just 2.5 - 3dKH over the reference fluid that its testing
7. For tank water Hanna checker gives me a dKH of 8 and KHD gives me a consistent 10 - 10.3

Saltwater is Tropic Marin Pro made up to std strength i.e. 1kg/30litres which should be about 7-8 dKH which is roughly what Hanna checker is saying

I really don't know what else to check, the only thing which is odd is the waste is being reported much higher than is being produced - waste on dosing pump 3 is showing as 1439ml in the container at most its 950ml - this has been consistently high

I've posted this on GHL's forum too but bigger audience on here, hopefully someone can explain why I'm getting a consistent high reading

I had the same issue, pick up a small scale from Amazon and measure with the scale, you’ll start noticing accurate results after couple of tests.

 

[Henryb9]

I matched mine with the trident when I had it and it was 2.4dkh off, and with the measurement with the scale it was the same exact.

 

[r21]

I had the same issue, pick up a small scale from Amazon and measure with the scale, you’ll start noticing accurate results after couple of tests.

Happy to try that but surely a graduated measuring cylinder should be relatively accurate and I've calibrated the pumps several times with close results each time

 

[Henryb9]

Happy to try that but surely a graduated measuring cylinder should be relatively accurate and I've calibrated the pumps several times with close results each time

Lol that’s what I thought it was also, I used a cylinder at first. But had to recalibrate everything with scale. My scale converts the weight the ML so it was easy. For the sample line put exactly the same ML you get from the scale that’s including with the filter. I filled everything from the ghl command center from the computer, so it didn’t ask for any water filter, if I remember correctly. So just input the total amount you get off that tube.

 

[r21]

Lol that’s what I thought it was also, I used a cylinder at first. But had to recalibrate everything with scale. My scale converts the weight the ML so it was easy. For the sample line put exactly the same ML you get from the scale that’s including with the filter. I filled everything from the ghl command center from the computer, so it didn’t ask for any water filter, if I remember correctly. So just input the total amount you get off that tube.

Just ordered some scales accurate to 0.1ml - did you find the weighed value to be higher or lower than the measured value by tube length or measuring cylinder? - I just can't see how its vastly different based on an 80ml sample size. My current reading is 2-3 higher so that's 20-30%, would that not translate to sample size/ reagent used being 20-30% off. Calibrated sample pump is 38.5ml/min so it would have to be wrong by around 7.5 -11ml, guess smaller margins on reagent as its only 6.5ml/min so 1.3- 1.95ml so I guess that's the most likely if it is that

 

[Henryb9]

Just ordered some scales accurate to 0.1ml - did you find the weighed value to be higher or lower than the measured value by tube length or measuring cylinder? - I just can't see how its vastly different based on an 80ml sample size. My current reading is 2-3 higher so that's 20-30%, would that not translate to sample size/ reagent used being 20-30% off. Calibrated sample pump is 38.5ml/min so it would have to be wrong by around 7.5 -11ml, guess smaller margins on reagent as its only 6.5ml/min so 1.3- 1.95ml so I guess that's the most likely if it is that

So for the tube length measurement with there calculations it was higher, when I used the scale I got a lower reading. Also for the pump calibration also I got a lower reading compared to using a cylinder, but I just don’t know how much. And I was comparing my alk readings to the trident (which was really accurate) when I had mine, that’s when I noticed the high readings from the khd.

 

[r21]

I've just used some basic kitchen food scales and that came out at 4ml for the reagent but scales not accurate to decimal points. I've turned off measurements until I get scales tomorrow

 

[Henryb9]

And the Way I measured mine was, I filled up the sample line with water till the out section of the doser head and reversed back the water to the scale container till everything was dispensed out and measured it.

 

[Henryb9]

I’ve spent days figuring it out lol, they should all come with scales! It makes it easier.

 

[Lasse]

If the readings is consistently off - you can use this feature

Sincerely Lasse

 

[Lasse]

I alway use a scale and run between 3 and 5 calibration runs and take the average of it as my volume / minute

Sincerely Lasse

 

[r21]

If the readings is consistently off - you can use this feature

Sincerely Lasse

Thanks, I've seen that option but the documentation also states something along the line if you use it you are moving away from lab grade configuration. Also I'd much prefer it to work correctly i.e. measure the reference solution at 7.5 +/- 0.2 dKH

 

[Tristren]

Thanks, I've seen that option but the documentation also states something along the line if you use it you are moving away from lab grade configuration. Also I'd much prefer it to work correctly i.e. measure the reference solution at 7.5 +/- 0.2 dKH

After calibration (with scale), and the settling in period which is also advised, they had me use the adjustment feature. By about 12% if I recall correctly. Indication was it would affect anything and it hasn't to my knowledge.

I agree it would be nicer to have it lined up with the calibration fluid but i suppose it is compensating for some constant in my case (length of sample tube maybe as mine is a bit long).
Also make sure to factor in the volume of the in line filter...

Tony

 

[r21]

After calibration (with scale), and the settling in period which is also advised, they had me use the adjustment feature. By about 12% if I recall correctly. Indication was it would affect anything and it hasn't to my knowledge.

I agree it would be nicer to have it lined up with the calibration fluid but i suppose it is compensating for some constant in my case (length of sample tube maybe as mine is a bit long).
Also make sure to factor in the volume of the in line filter...

Tony

I'll be disappointed if I have to use the adjustment after spending hours calibrating and purchasing reference fluid and scales

 

[r21]

Calibration differences based on weight
Reagent cylinder 6.5ml/min Weight 4.4ml/min
Sample cylinder 38.5ml/min Weight 37.9ml/min

 

[Henryb9]

After calibration (with scale), and the settling in period which is also advised, they had me use the adjustment feature. By about 12% if I recall correctly. Indication was it would affect anything and it hasn't to my knowledge.

I agree it would be nicer to have it lined up with the calibration fluid but i suppose it is compensating for some constant in my case (length of sample tube maybe as mine is a bit long).
Also make sure to factor in the volume of the in line filter...

Tony

Mine was accurate without any adjustment, could be wrong calculation.

 

[Lasse]

When you calibrate with reagent fluid pump - I hope you use the reagent as a liquid. I use to make 3 - 5 calibration runs - take the weight and divide with the number of runs. The difference for the reagent would play an important role.

Sincerely Lasse

 

[Kyl]

How is your sample intake routing handled? Is the filter mounted for horizontal water draw? Is your KHD mounted above the doser 2.1?

There are a lot of factors that can mess things up with the KHD. If everything is operating properly (measured and calibrated) it will be near dead-on with an accurate reference standard.

 

[r21]

When you calibrate with reagent fluid pump - I hope you use the reagent as a liquid. I use to make 3 - 5 calibration runs - take the weight and divide with the number of runs. The difference for the reagent would play an important role.

Sincerely Lasse

Yes, I use the reagent as the fluid to calibrate - I doubt 0.1M acid has a particularly higher density than water but just in case I did use it, just as I used tank water for the sample line,