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mhurley
09/18/2017, 07:46 AM
I'm having an issue in my system (lost all my torches and hammers in the last week) so I've done 3x10G water changes over the weekend.
This morning, I just ran 3 back to back phosphates tests with my ULR, (fresh battery last week), reagents are good until 7/2019.

13 ppb
21 ppb
1 ppb


I mean....come on....


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Aquageek450
09/18/2017, 07:58 AM
make sure you rinse the tube out with RODI water before you use it. It is very sensitive to any contaminants. Also once you add the reagent do not shake it, but turn it up down a few times to mix it up and then tap the glass to get rid of as many bubbles as possible because they will affect your measurement.

mhurley
09/18/2017, 08:36 AM
Yep, I do.

Curious...the reading that gets taken I assume it shoots the light across the tube to get the reading right? Not from the bottom...

mcgyvr
09/18/2017, 10:00 AM
Yep, I do.

Curious...the reading that gets taken I assume it shoots the light across the tube to get the reading right? Not from the bottom...

I'll assume its like the alk tester and yes it shoots light through the side..not bottom..

mhurley
09/18/2017, 10:04 AM
Assuming that's the case, I have a hard time with the "bubble" theory. I've never seen bubbles on the side. Either top or bottom if ever. And 3 minutes of settling before it shoots lets the entire sample settle out.

Just thinking out loud.


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mhurley
09/18/2017, 10:07 AM
Also if you get any bubbles on the side, your vial is dirty. Just like if you're ever served a beer with bubbles on the side. Send it back cause that glass is dirty. ;)



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mcgyvr
09/18/2017, 11:27 AM
Run some more tests.. making sure to have a clean/bubble free sample..

If its still "all over" then something is up.. If not its a "fluke" and could have been any of the reasons above or something else...

Dan_P
09/18/2017, 12:51 PM
Hanna readings are "bouncy" but most people don't notice this because they take only one reading at a time. The accuracy for the Checker is +/- 5 ppb +/- 5% of the reading.

If the true phosphate level was 13 ppb, you would see a reading between 7 and 19 ppb. For a true value of 21 ppb, you would see a value from 15 to 27 ppb. For 1 ppb, the range is 0 to 6 ppb. Using matched vials, I have taken 7-13 repeated readings of the same solution and found that two standard deviations in the readings to be close to the +/- 5 ppb +/- 5%. I now take 3-5 readings per test to get a better idea of the true measurement value.

Of the three test results you obtained, the 1 ppb might be an outlier. The other two values can be averaged for a mean value of 17 ppb.

Why the outlier value? If you are not positioning the vial exactly the same way for the blank test C1 and the test C2, slight imperfections in the glass can scatter the light and throw off the readings. Finger prints can absorb light and do the same thing. Vigorous shaking after reagent addition can produce tiny bubbles that adhere to the sides of the vial, possibly scattering the light beam. Floating debris from an unclean vial, debris in the test sample or from a contaminated chemical packet can introduce light scattering particles.

My guess is that the Checker is OK and you just ran into the real world of analytical chemistry :-)

Dan

dubmaneh
09/18/2017, 12:58 PM
I've read that the vials are not perfectly shaped so if you change orientation from the calibration to the test it can alter readings.

Using a thin permanent marker, make a mark on the top/neck of the vial and on the meter. This way it is always aligned in the same place.

Also tap the vial on a countertop to get rid of any micro bubbles and make sure there are no fingerprints on the glass.

These tests are measuring in ppb so are very sensitive. The above worked for me.


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bertoni
09/18/2017, 03:53 PM
Measurement problems are a constant source of problems. Trying some of the ideas given here might help get more consistent results. Honestly, I don't have any much better answer. If you don't mind spending a fair chunk of change, enclabs.com will run tests, but I'm not sure that it's worth it. Have you tried the Hash PO-19 kit? It requires a visual comparison, but it's a good quality kit.

mhurley
09/18/2017, 04:32 PM
Never thought about glass variations.

Oh and just ran it again. 0ppb.

bertoni
09/18/2017, 05:33 PM
Some days, it just isn't worth chewing through the straps.

mhurley
09/18/2017, 05:35 PM
^troof

tmz
09/19/2017, 08:41 AM
These conversion charts for the hanna ulr checker are helpful ;one includes error rates:

http://www.pny.se/aquarium/

Mohammed
09/20/2017, 02:02 PM
Hi, any suggestions on cleaning the vials, i did read something about citric acid but cant recall the directions.

bertoni
09/20/2017, 03:41 PM
Citric acid should be fine. I suspect that vinegar would be a reasonable choice, too, following by a good rinsing.

tmz
09/21/2017, 10:18 AM
Rinsing the vials several times with tap water and then several more rinses with ro/di water after each use ,leaving a drop or so of ro water in the vial before capping it for storage ,keeps mine clear.

hkgar
09/21/2017, 11:27 AM
I always make sure the 10ml mark on the side of the vial is facing out when I insert the vial to make sure I always have the same orientation.

catman78
09/22/2017, 10:47 AM
There's a thread hanging around for this..
Basically this
Use the same vial for both steps of test.
Open packet and have ready to pour in vial. I cut it diagonally and gather up powder in one spot.
Get a separate timer and set to 3 minutes.
Complete C1 step and start separate timer.
You have three minutes to dissolve powder into test tube. I find 2 minutes if enough for swirling/mixing.
Start C2 count down.

I get fairly good results. I always test twice and average them.

mhurley
09/22/2017, 01:05 PM
There's a thread hanging around for this..
Basically this
Use the same vial for both steps of test.

Interesting. The way you phrase this is that we are supposed to use both vials (but recommending against that).
Iíve never used both vials for one test. I assumed the second vial is merely a back for when you drop and break the first one, not that itís supposed to be used.

hkgar
09/22/2017, 01:39 PM
Sadly, there are those, hopefully only a very small few, who use both vials.

tmz
09/23/2017, 10:10 AM
I always use the same vial for a test.

dubmaneh
09/23/2017, 03:39 PM
Sadly, there are those, hopefully only a very small few, who use both vials.



Haha. Sadly I must admit that I did that the first time. [emoji23]

Once i figured it out though I get pretty reliable readings.



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Dan_P
09/23/2017, 04:24 PM
Sadly, there are those, hopefully only a very small few, who use both vials.

In general I agree, but it isn't absolutely true that you can't use two vials.

Using two vials is the only way to quickly read the same test solution more than once to get a standard deviation (I know, yuk!). The catch is that the vials need to be matched by finding the sides that have equal transparency. Sometimes this can't be done with the supplied vials, but I have more than one Checker and fnding a matched set was easy.

mhurley
09/25/2017, 02:43 PM
I guess I don't understand what is being discussed regarding the 2 vials.

Are you suggesting that once I run the test to pour the contents from vial 1 into vial 2 and run the reading again?

mako61
09/25/2017, 03:25 PM
I think what he means by using 2 vials -

take 2 vials that measure the same with just water -
use one vial to zero the meter -
use second vial with test solution -
zero meter with first vial - read the test solution in second vial

repeat this a few time to get an average reading of test solution with out having to redo test solution.

I did that at first myself, but i was unsure if using 2 vials added more error than the average helped. I did notice the number changed a good bit with this method try to try which was a bit disappointing.

outssider
09/25/2017, 04:41 PM
+1...

fill both vials with tank water. add the reagent to one. turn the vial up side down/right side up gently to mix the powder. after it's mixed well wait a couple minutes for any bubbles to dissipate. put the unreacted sample in the checker for the first read then put the reacted sample in for the second read. you can do this many times to get many readings off the same samples. This will only work well if the two vials are matched in clarity and diameter.

catman78
09/26/2017, 04:36 AM
See bold below.
Use one vial and a separate 3 minute time(Phone, kitchen timer, etc.)

See post 128

http://166.78.194.238/forums/showthread.php?t=2363251&page=6

"I reckon I have got a process through practice which works for me. I can get exactly the same reading now 2-3 times in succession...used a few packs of reagent getting there....but am confident now with the 736 Checker.

wash cuvette well in sample water and fill to 10mls, put cap on
polish outside with cloth, tap firmly on table a few times to free bubbles
insert and align "10" marking to front..anywhere will do ...just remember
close unit..press nothing yet

fold small dry paper down centre
empty a reagent packet fully onto paper, spread along the fold a little

press button to power on
press button again to set unreacted baseline (then shows C2 for 3 mins then turns off and you waste the reagent...but there is plenty of time to do this)
remove cuvette, remove cap
wipe top rim of cuvette with cloth or tissue to dry it..(important)
pour reagent in...dry top means paper doesn't wet and stop pour.
close and shake well 1.5-2.0 mins (some people say gently..?)
polish glass with cloth
tap on table 10 times holding by lid to free micro bubbles
insert in checker aligned same as before
hold button in to start 3 min reaction time
leave on table...do not pick up..allowing to settle clear
see Phosphorus reading ppb after 3 mins
multiple by .03066 if you want Phosphate equivalent

I had a bad box of reagent but am now good... you just have to validate your reagent in some way..my bad one just read 0,1,0 etc...so I was confident it was bad....I knew I had a phosphate problem as my Red Sea Pro PO4 test was saying about 0.10...but hard to read. I now get 28 ppb Phosphorus from the 736 and can repeat it....multiplies out to .086 phosphate equivalent which is where I would expect after a using bit of Phosphate Killer.

Now works for me."