KH Readings

I have had my KH Director up and running for a couple of months. It took a week or so but we finally got it dialed in. Every reading matched my Hanna exactly, every time. At that point I turned on the controller section. It worked very well, was extremely impressed... Then a couple of weeks ago, I received a warning that my KH was out of range. (I'm set for 8.5, with a low of 8 and a high of 9) The reading was 14. So I ran home and kicked off a test and what I found was one of my heads (the water sample) had gone out. I've heard that this happens occasionally and while not what I wanted it certainly was better then my KH going from 8.4 to 14 in 4 hours. I pulled off the cover, rollers and spindle. There were pieces of the blue cover on the roller as if it had melted it off. I have one unused head on one of my controllers and I took those parts and rebuilt the head. It worked fine and not only that when I calibrated, it was the same calibration as before. I went thru the initialization procedure and then ran a test. The reading was 11. Well, I always ignore the first few readings until it gets dialed in as the first reading is always trash. And it did dial in, between 10 and 11. No matter how many times I go thru complete calibration, starting from scratch, the readings are now always in this range. My Hanna still reads in the 7 to 8 range and I have checked my multiple other brand tests. The tank looks great, corals are happy, these readings are just off. Now, I could always adjust the reading, but I know it is capable of being exactly on the money. I have recalibrated the probe (ever had a probe go bad?), all the pump heads multiple times, remeasured the sample line (that never changed but it has to be something) and it now it only measures my KH in this range. (see my graph attached. the high point and low point were immediately after a calibration) I was really stumped. Suddenly I realize that there was something different. When my head crashed, and I was recalibrating i did run out of my first bottle of reagent and i had to pop a new bottle that I had ordered online from a place I had never ordered from before. Could that be it? Weren't there originally issues with reagent. If so, are there certain lot numbers. Has this exact thing happened to anyone else?
Thanks in advance.
Jeff

Attachment 10984

Have you emptied and flushed the measurement cell?

Please also check this FAQ: https://www.aquariumcomputer.com/kh-...oubleshooting/

Thanks Thilo,
Yes, I have emptied and flushed the measurement cell so many times that I actually affected the salinity on a 300 gallon tank because of the top off system. My calibration is exact using a insulin syringe and by weight using a lab scale to verify. I have ordered a couple of bottles of fresh reagent and they added the flex PVC line. (I am using one but it's one I already had) It is getting a large amount of air in the reagent line and even tho it is just building a bubble beneath the head, I can only assume that there is some air getting by and into the chamber. Besides the head going out, the only difference between my dead on exact readings and the readings that are 2 dkh apart is the new bottle of reagent. Is that possible that is the cause?

The first version of the reagent was more prone for air-bubbles.
The newer reagent has a light blue color.

What you can do against the air-bubbles is described in this post: https://forum.aquariumcomputer.com/s...0657#post80657

I believe the reagent in the "new bottle" is light blue. My first bottle was the 500 ml bottle that came with the Ultimate kit. It was perfect. No air what so ever. When it arrived with the kit, it sat for a few weeks at room temp (about 69°) before being put into use. It provided impressively accurate readings. When the new bottle arrived it sat in the mail box for several hours and the other part of the day on a hot truck. Here the days are in excess of 100°. The bottle was immediately placed into service at a room temperature more then 30° cooler. Is this a temperature change issue? Was there a change in chemistry between the first and second batch?

The "new" blue reagent has exactly the same acid concentration as the previous one, so the KH result must be the same.
The only difference is that the newer bottles are treated to avoid micro air bubbles (the bottles are slightly warmed and shaked).
Besides that, the new reagent is out for about half a year and nobody reported wrong measuring results caused by it, our internal test show perfect results, so we assume the reagent is OK.

The temperature change is an issue, but it will disappear after a few days.

To make it short: There were a lot of events at the same time, it is hard to say which of them caused the issue.

We have to take this into 2nd level support. Email comes.

So, I received 2 new bottles of reagent and the replacement PVC tubing from Marco. I changed out the PVC tubing with no affect. As for the bottle of reagent, it is close to empty so I'll just run it out. Not going to waste the money. My range is still a steady 10.7 to 10.9 so I went ahead and adjusted the viewed number by -24%. I now measure right on with my Hanna checker, Red Sea and Salifert. I check them frequently. I guess if this is how it has to be, I can live with it. I am curious tho to see what happens when I change to a fresh bottle of reagent.

Just a heads up, the KHD will stop testing once there is 50ml or less reagent left in the bottle. You may want to have another bottle ready before you get to that point. ;)