KH Director readings always the same, no matter what?

[Laith_61]

Hello,

I installed the KH Director with a Doser 2.1 (Slave) two days ago, following all the directions in detail: calibrated pH probe (twice), calibrated the three pumps (sample water at speed setting 3, reagent at speed setting 0 and waste water at speed setting 3). I then vented the reagent tube and flushed the measurement cell according to the instructions. I set the unit to use 80ml water samples and input the length of the water sample tube (both from the sump to the doser and from the doser to the Director, total 116cm). At the moment I am not using the Director for KH control as I wanted to ensure correct KH measurement first. The Director is connected to my Profilux 4.

The first manual measurement returned a result of KH 6.6. I compared it to a Hanna KH checker with returned a value of 6.8. Using the Director I added a manual dose of Carbonate to raise the KH by 0.5. An hour later the Director measurement was 6.7.

I also increased the standard dosing of Carbonate by about 15%.

Last night the Hanna checker showed a KH of 7.1 while the Director was at 6.6. I added another manual dose of Carbonate.

This morning the Director measured 6.7.

I decided to check both the Director and the Hanna against the GHL KH 7.5 Reference. The Hanna showed a KH of 7.5. The Director showed a KH of 6.7.

In all of the tests subsequent to the first one, I kept an eye on the "actual pH" reading of the Director and the the pH would descend constantly during the test, which I take to be the normal behaviour.

I then vented the reagent tube, flushed the measurement cell and completely flushed the measurement cell.

Another manual measurement and the KH Director gave a reading of 6.6. During the test the "actual pH" measurement started at 7.41 and descended to 4.35.

So for some reason the KH Director is not able to give readings other than 6.6 and 6.7, no matter what the sample liquid is at...

The reagent tube (the "stiffer" tube that came with the Director) is about 25cm long and goes straight down from the doser pump to the bottom of the reagent bottle, no curves or loops. The vent tube is not kinked or obstructed.

Any ideas what the problem could be?

Thanks,

Laith

[Vinny]

Hi,

Can you please post a screenshot of your KHD settings page?

When you entered the length of the water sample tube, did you also include the length of the beige tube inside the doser head?

[Laith_61]

Hi Vinny,

Thanks for your reply.

Ah! no I hadn't included the length of the beige tube... is that about 12cm? I will add that and try again.

Here are the screenshots of the KHD settings. They are from myGHL as I'm not at home at the moment and they are in three parts to show the whole page.

114481144611447

Thanks!

Laith

[Laith_61]

I added 15cm to the sample tube length which changed the tube sample volume from 15ml to 16ml and took another KH measurement: still 6.6.

20mins later I took a KH measurement with the Hanna: 7.5

I don't see how this could in any way be related, but the KH Director time has always been one hour off (the Profilux time is correct). The KHD always measures at the correct time (set in "always measure at this time") but consistently reports the "last measurement taken" as one hour ahead, ie 12:45 instead of 11:45. Could this indicate some type of malfunction?

[Laith_61]

And just to be thorough, here are screen shots of the three dosing pump settings...

114491145011451

[Laith_61]

Just realized the screenshots I attached are tiny.

Here they are again, hopefully more readable!

11452114531145411455

[Ziemowit]

Hello,
I have an identical problem.
Ziemowit

[Vinny]

Laith,

The measurement times are based on the time zone settings in the General settings page. If this had not been set, you will not get correct measurement times. It is not a malfunction.

With regards to the same readings, can you please empty the measurement cell and remove the KH probe?

Check the high and low ranges of the probe by sitting the probe in pH4 and 7 solutions


What are the results?

[Laith_61]

If the time issue has no effect on the KH measurement, then I will bring that up in another thread...

When in the pH 4 solution, the "Current Value" shows 4.11
When in the pH 7 solution, the "Current Value" shows 7.11

Is it a calibration issue?

[Laith_61]

I put the probe in my tank water and it showed 8.08 while the pH probe connected to the Profilux 4 is showing 7.93.

I will re-calibrate the KHD probe and take another KH measurement.

[Laith_61]

I recalibrated the KHD pH probe. It took me three tries to calibrate at pH 4: I got a "calibration failed" error message on the first two tries. The calibration at pH 7 worked the first time.

I then took a measurement using the KHD and the Hanna. Hanna 7.7 KH and KHD 6.8 KH...

So I guess it was not a calibration issue. What now?

[Laith_61]

By the way, the rise in KH shown by the Hanna checker is to be expected: as I mentioned, I increased the daily Carbonate dosing by about 15% in order to help raise the KH from the initial measurement of 6.8.

What is frustrating is that the KHD is not reflecting that increase in dosage...

[Vinny]

Please open a support ticket and reference this thread so we can provide further assistance.

[Laith_61]

Ticket opened...

[Ziemowit]

Hello,
I have an identical problem.
Ziemowit

Hello,
Does anyone have an oxygen probe connected?
Ziemowit

[esmerok]

Ticket opened...

Hello, i have now same problem, do you fix it?

[Laith_61]

Well, yes.

I think one of the problems of moving to a KH control system to measure and control KH is that these systems use a completely different methodology to measure KH than what the average hobby test kit does: titration of a reagent with pH measurement instead of a colour titration (either visually or via a colour detection system such as a Hanna Checker). In fact, from what I have researched, this is one of the most accurate ways to measure KH.

My conclusion is the following:

1. It does take the KHD several if not quite a few measurements to "settle" down and start showing consistent results as well as showing correct changes in KH.

2. You have to accept that even if the KHD readings seem to be different from your usual KH test method, once they show consistent results, you should trust them. For me, this was the most difficult "psychological" obstacle to overcome as you can see from my posts.

3. More important than the actual KH figures is the ability of the KHD to measure and, through it's control capability, keep the KH within a set level... once again consistency.

So I have set the KHD to control my KH with a nominal value of 8 KH and it is doing a good job of doing that (using the adaptive mode of control). My Hanna KH checker may not show 8 KH (I haven't tested that) but even if it showed 7.5 it still means that I now have a way of keeping it at a consistent level of 7.5...

That is enough for me and my corals are not showing any adverse effects after two weeks of the KHD controlling the KH.

Not sure if that answer is as clear as it could be but I am now happy with what the KHD can and is doing!

Laith