Hanna phosphorous frustration

[Velodog2]

So I got the Hanna low level phosphorous checker a couple months ago and at first was somewhat pleased, but have since experienced growing frustration with this flawed product.

My specific issue recently is that I've discovered that if I retest the same water sample in the unit several times I get highly variable results.

Because of the battery saving time out feature I have given up on using a single cuvette for zeroing and testing and now use one cuvette to zero and the other to test. This is also partly due to the time it takes to completely empty those ridiculous packets the reagent comes in, but I won't go into that now. I figure using two cuvettes may reduce accuracy slightly, but shouldn't significantly affect repeatability.

Since I am using two cuvettes I can re-zero and retest the same water multiple times. I have repeatedly found that the first reading I get on a sample is 2-3 times higher than subsequent readings. For example this morning I tested and got 30 ppb phosphorous on the first try. Using the same water samples in the same cuvettes I then got readings of 10, 11, and 12. I should perform a full R&R study, but don't want to use up the expensive reagents, or frankly spend the time.

Since the later readings are more repeatable I am inclined to believe they are more accurate. Perhaps the time allotted for mixing the reagent is insufficient for fully reacting it? Why do we have to do the work of figuring out this machine? I'm wishing I'd just gotten the Redsea kit at this point.

 

[howaboutme]

That's interesting. I wonder if there's a "shelf life" to the regents once they are open. I have to check the instructions again.

What I do is use both cuvettes. I fill them both up w/ water. Then I fill one of the cuvettes w/ the regents, which includes the mixing time. Then after all of that, I start the process of zeroing and testing. This way, you don't have to ever fight to do all of that within the time it takes for the checker to time out. I realized this after my first time.

 

[glb]

That's interesting. I wonder if there's a "shelf life" to the regents once they are open. I have to check the instructions again.

What I do is use both cuvettes. I fill them both up w/ water. Then I fill one of the cuvettes w/ the regents, which includes the mixing time. Then after all of that, I start the process of zeroing and testing. This way, you don't have to ever fight to do all of that within the time it takes for the checker to time out. I realized this after my first time.

I do the same thing. The auto shutoff on this one is a designing flaw. Plus it's hard to get all the reagent out of the packet. Wish they would put out a liquid reagent.

 

[Velodog2]

Yes to all that. But have you ever retested your samples after the first time?

 

[howaboutme]

I just did a quick search and found an interesting thread on another forum here. Not sure if I can link another forum but if not, mods, please edit my post.

There is one post that is the most helpful:

Start out with only 1 vial. Make sure it is clean. Make sure you always discard old solution, rinse, and store it full with RODI water. This prevents staining or buildup on the glass that could influence the colorimeter.

Dump out the RODI, and rinse several times with aquarium water. Then fill to line. Make sure that there are no particulates in the vial.

Dry and clean the vial taking care to remove any finger prints. Put the vial into your meter and zero out. Note the orientation of the vial by paying attention what direction the printing on the vial is facing.

Using the same vial, put the reagent into the vial making sure that you got all of it in. Do not let your fingers touch the inside of the pouch or the reagent. Don't use a different vial as this could produce different results.

Continue to invert vial to dissolve the reagent. Don't shake aggressively because it will create air bubbles. Using a stopwatch (download an app) or using the timer feature on your microwave (I do my testing in the kitchen), pay attention to when your 3 minutes before auto shutoff expires. When you get close, stop shaking and continue by rotating in a spinning fashion to keep it moving while cleaning the vial with a cloth.

Put the vial into the meter making sure you install it in the same orientation and start the cycle.

After the cycle is completed, rinse and store the vial using the previous mentioned method.

Note: If you intend to do a recheck, prepare a new solution. If you retest the already tested solution you will NOT receive the same result because the reagent had a longer time to react.

I bolded the last sentence but I can't verify that remark though that person is not the first to say that. Also note the suggestion of keeping the orientation of the cuvette the same.

Thanks for the post, this has opened my eye a bit and will adjust my own testing.

 

[jt17]

Are you holding the button down to start the 3 minute timer?

Bummer about needing different vials, I've been using different vials for testing because I use the 10ml tank water for the phosphate, while the powder dissolves in another vial, then I use that vial for alkalinity. Much quicker.

Maybe not a perfect tester, but as far as I know it's the best we've got.

 

[pickupman66]

Mine tested .04 night before last. Then last night it was .20. I had not fed my fish in between readings. Wonder if I could pour a little water into the packet to get the remaining dust out.

 

[ingtar_shinowa]

From my testing I know the reagent not being fully dissolved affects the test greaty. I heard the longer it sits the high the reading and it has more time to react. So I usually test a few times until I get to low tests. I dont know how much science there is in that but whatever, my po4 is elevated anyway.

 

[pickupman66]

Just tested. .05. Hope that is right... I like it

 

[howaboutme]

I just tested too but this time I used only 1 cuvette and just had the regent ready to be poured into the cuvette when asked. I also paid extra attention in keeping the glass clean and wiped w/ glass cloth as well as made sure the cuvette was oriented in the same direction. I got a number not much different from previous tests. I will still continue to perfect the 1 cuvette method though.

 

[Reefltx]

I just tested too but this time I used only 1 cuvette and just had the regent ready to be poured into the cuvette when asked. I also paid extra attention in keeping the glass clean and wiped w/ glass cloth as well as made sure the cuvette was oriented in the same direction. I got a number not much different from previous tests. I will still continue to perfect the 1 cuvette method though.

Same here, I get pretty consistent results with mine. You get 3mins for putting in the reagent and mixing, after you hold C2, you'll get another 3min count down. So, a total of 6mins which is plenty IMO. I have a timer watch going when mixing so I don't go over the limit.

 

[Keithcorals]

I have the phosphorus and the phosphate checkers and have gone through over a hundred reagent packets. All the tests I've done have been withen the margin of error. Even when using reagents packets from different batches of reagent. When I test I always have my reagent ready befor zeroing the checker and make sure the outside of the cuvette is wiped clean before zeroing and after the reagent is added.ive performed the test with two cuvettes and still got consistent results. I did a test a while back where I did 10 readings with 1 water samples per day for 10 days. The first time I zeroed the checker was done with the cuvette that would have the reagent added and then I used the second cuvette to zero it for the next 9 readings. After 10 days and 100 readings all were withen the margin of error. I wish I still had the results but I think the notepad I had them in was thrown away. After that I'm more than confident that the checker is not a bad piece of equipment. But there's always going to be a defective one or two of just about anything mass-produced.

 

[Velodog2]

I just did a quick search and found an interesting thread on another forum here. Not sure if I can link another forum but if not, mods, please edit my post.

There is one post that is the most helpful:



I bolded the last sentence but I can't verify that remark though that person is not the first to say that. Also note the suggestion of keeping the orientation of the cuvette the same.

Thanks for the post, this has opened my eye a bit and will adjust my own testing.

That is a great thread! I read it entirely. It ends up focusing on reagent quality control and Hanna's poor response. The company does not come out looking very good, especially when you take into account the issues I heard they had with their alkalinity reagent. I will be paying attention to my lot numbers and stil may end up with a Redsea test kit.

But I don't think the reagents are my current problem. The issue with wait times you quote seems to be one of increasing readings with time as the reaction progresses, whereas mine seem to decrease then stabilize. I kinda think that a good test would allow the reaction to go to completion. Otherwise you are guaranteed some inconsistency just due to timing. And it just doesn't make sense that you would want to measure a partially reacted sample.

Anyway, again back to my issue (besides my insomnia). I'm going to guess that I may have micro air bubbles from mixing, or some residue that settles. That could explain the higher readings I get initially, followed by a steep drop off and then consistency.