How important is it to get /all/ of the Hanna dry reagent in the sample?

[Breadman03]

Consistency>Precision

Obviously, we want to be relatively precise, but the most important thing is to be consistent. That will allow you to see changes and get them back to what works.

 

[bertoni]

I agree that consistency is more important than a bit of precision. Still, it'd be nice to have kits that are easier to use.

 

[ReefTeacher]

Doesn't precision mean consistency? Are we talking about accuracy?

 

[Breadman03]

Doesn't precision mean consistency? Are we talking about accuracy?

Not necessarily. There is a margin of error in everything, and we really don't know what our margin of error is when we (typically amateur) use hobbyist grade (read:relatively cheap) test kits. The greatest factor that we have control over is our consistency in their use.

For example, I've read quite a few complaints about Red Sea and Salifert test kits giving quite different results. I use both, mostly so that I could have a second, unrelated kit to confirm any strange result and I wanted to compare them to see which I prefer. With my kits, I've been getting near identical results. It could be that my particular lots match well, or it could be because I do my best to follow the instructions to the letter.

Someone else would possibly get a slightly different result on my tank with my kits. Why? They might read the plunger position slightly differently than me, or their eyes could perceive a color change differently. They might shake the sample more or less. All of those factors might change the result we get. After it's all said and done, so long as our actual values are within an acceptable range, keeping those values consistent is more important than knowing the actual value.

 

[Dan_P]

Doesn't precision mean consistency? Are we talking about accuracy?

Strictly speaking, consistency is precision. Accuracy is about closeness to the truth. It is relatively easy to estimate consistency or precision by repeating the measurement several times. Estimating accuracy is more involved, in this case, requiring the measurement of a standard of a known quantity.

The hobby test kits seem to do a good job with accurracy, but suffer in precision because we have to interpret the color by comparing it to a chart. This is why using a Hanna checker improves consistency (we don't actually "know" that it improves accuracy. We usually take the vendor's word for it). Also, the fussier the procedure the more gottcha's there are that decrease consistency and possibly even accuracy. For example, a procedure that requires pouring a powder into a narrow neck bottle.

 

[bertoni]

Yes, I should be more careful with the language. Technically, precision is keeping the readings close together, and being able to distinguish small changes. Accuracy is, as has been stated, how close the measurement is to the truth.

Generally, our kits have a fair amount of noise down at the bottom of the phosphate range. I wouldn't worry about small changes, but focus on keeping the level within some reasonable range of results.

 

[Buzz1329]

Hannah should produce the reagents in a tablet form. Just drop the tablet in the vial and you are good to go.

Agreed. I have found it almost impossible to get the reagent into the tube within time provided. RedSea calc test uses powder and tiny spoon as part of testing process. IT WORKS. Why can't Hannah do something like this?

 

[Buzz1329]

This easily answered. Carefully pour out the entire contents of a packet onto a piece of wax paper. Using a razor blade carefully gather the powder into a shallow pile and then form a square, while trying to keep the depth about the same across the square. With the razor blade divide the square into two unequal piles, say 1/4 and 3/4 the original size. Run two separate phosphate tests using these quantities. Compare these two results to your usual full packet results. Post the results so we know what happened. Thanks!

Thanks.

I applaud your ingenuity in finding a way to work around the basic problem: the stupid packets that Hanna provides with kit provide inconsistent results for most customers.

 

[Buzz1329]

I don't understand why they don't sell it like the salifert reagent for calcium/nitrate/magnesium where you get a little bottle and a little scooper.

The individually packed powder seems more expensive to produce and it is ridiculously dumb to use in practice.

I just assume I am always going to be a bit off -- having them say 95% vs 99% affects the reading isn't helpful. Helpful would be knowing if it meaningfully impacts the reading..

Agreed

 

[Buzz1329]

I'm sure Hanna took into account the residual still remaining in the packet when filling them to the designated level. What I do is hold the packet by a corner and flick the two top sides with my finger to loosen anything caught in the top creases of the packet. I then cut the two side as indicated on the packaging and then pull the two remaining seams to the edges. I'll then tap the sides with scissors to loosen anything still in the crease. Then fold a nice crease and pour it in.

Only once did I spill some of the Ca powder, which threw my results off. The Ca reagent is more course and pours out better then the super fine Ph reagent. But if you're careful I think you're getting all that's needed to conduct the test.

I'm sure this works for you, but why the hell does it have to be so difficult to perform a test using the Hanna PO4 kit. I've stopped using it because I cannot get anything near consistent results.

 

[Buzz1329]

Or you could reduce your testing noise by testing in triplicate and averaging the results...

That seems like a reasonable response for a test kit that a lot of users find incapable of providing accurate results with one test. But why should we have to test 3x to get a (possibly) accurate result? That just triples the cost of the test kit.

Mike

 

[Buzz1329]

i agree that consistency is more important than a bit of precision. Still, it'd be nice to have kits that are easier to use.

+ 1

 

[Dan_P]

Transferring powder is a fussy operation. A tablet might work but adds cost to the product. Additives needed to manufacture a tablet might make it too large for the vial opening or interfer with the test itself.

I just started looking at the ultra low PO4 system right now to see if I can reduce the test volume to 1 mL and still get consistent results. I mention this because I found that the powder flows easily and does not clump. I found it takes only a bit of cutting and creasing of the packet to get all the powder to dump out into a small opening. I imagine if you do the cutting and folding before setting the timer, this would give you more time to tap the powde in to the bottle.

 

[madweazl]

I'm sure this works for you, but why the hell does it have to be so difficult to perform a test using the Hanna PO4 kit. I've stopped using it because I cannot get anything near consistent results.

Phosphorus
I have shaky hands and the harder I concentrate on what I'm doing, the worse it gets. With that said, I've only screwed this test up two times (one where I knocked the cuvette over completely LOL). I've found cutting along the line indicated on the packet and folding it in half at the rounded corner has worked really well to get the vast majority of the reagent in the container. Once I get that in there, I'll turn the packet upright again and tap on the sides to dislodge any remaining reagent and then I dump that in there and test.


Calcium
I was having pretty good results with this kit until last weekend when I got three consecutive readings around 490 when I believed the truth to be around 455. I contacted Hanna (outstanding customer service by the way) and they sent a .5ml syringe along with some deionized water to try out. The results were back inline with reality (around 440 now) and I confirmed the results with the Salifert kit. Wish I had rechecked with my own RODI water at the time to see if there was still a large delta but I got caught up with Battlefield 1 I guess. I'll have to try them back to back this weekend (this hadn't been an issue in past tests).

I do like the idea of a bottled reagent with a spoon for some of these reagents. For the Ca test, it would be nice to have something that eliminated user error for the .1ml of sample water but I think I've got a pretty consistent process down (with three tests I got 484, 495, and 497). Like others, I believe consistency is more important that accuracy. While I may not know the exact calcium levels in the water, if I'm consistent, I at least know the consumption and how much I need to dose to maintain consistency.

Alkalinity
I've noticed some "floaties" (lack of a better term) in the water when performing tests and was curious whether or not others have observed this? At first I thought they were from my water but last night I discovered they're coming from the reagent.
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[00101]

Pick up some gilson pipetmen (or some cheap chinese ones) a P10mL and a P200 should cover the alk, calcium, and phosphorus liquid measurements.

I haven't had any real problems with the phosphorus test. I open the packet before I begin the test. I flick the packet to move all of the powder into the bottom corner. Then cut open along the two lines and push them together to fold open the rounded corners. Its pretty easy to get all the powder in, bar the little bit of fine dust that coats the inside.

 

[Potatohead]

Alkalinity
I've noticed some "floaties" (lack of a better term) in the water when performing tests and was curious whether or not others have observed this? At first I thought they were from my water but last night I discovered they're coming from the reagent.
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I noticed that too... I haven't noticed it affecting the results. It gets worse as you get to the end of the reagent.

 

[BlackTip]

I noticed that too... I haven't noticed it affecting the results. It gets worse as you get to the end of the reagent.

I noticed the same thing. I called Hanna Instruments, and they said it is normal and don't effect the result.

 

[Dan_P]

Here is a quick study on the variability that I found with the ULR phosphorous checker. Using paired vials, one filled with tank water, the other a Hanna test solution of the same tank water, I retested the sample over a period of time. I know the instructions warn against letting the test solution sit too long before measuring it, but I found no indication of change in the results. The average reading was 5.7 ppb with a relative standard deviation of 37%. This certainty is consistent with posts that express frustration with variability.

I did notice tiny, barely visible bubbles forming part way through development time of the test. I was careful not to introduce any by vigorous mixing, rather I gently rocked the solution to mix in the reagent. I also marked the checker and vials to ensure that they were positioned the same way in the light beam every time. Because of this, I don't think the bubbles were the cause of the variability.

 

[tmz]

The packets are a bit tedious; however, keeping the poswer sealed in foil limits air contamination before use. The wax paper sounds like a neat method. Alternatively, I just snip off the top and peel back the side seams; crease the remaining flat square and use that as a funnel to the vial.

 

[ThRoewer]

Hannah should produce the reagents in a tablet form. Just drop the tablet in the vial and you are good to go.

^^This. It shouldn't be too hard to press the powder into a pill and it would definitely add to the precision.

Another issue are the vials with inconsistent glass thickness. You can run the same vial with the same liquid several times and you always get a somewhat different reading.