HighlandReefer
Team RC
+1 for the above post. 
Thanks for your time and efforts.
Thanks for your time and efforts.
Want more accuracy from your test kits???? Read this to find out how.
- Thread starter disc1
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disc1
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So I'm looking at ordering the big three from Hach. For those of you playing along at home, I have the shopping cart open in another tab and my total with shipping is under $100. They don't have tax included, and the magnesium standard is in HNO3 so it ships as hazardous. We'll see what happens. I may have to have it shipped to my work, but I tried to get it to my home just to see whether or not it's going to work. If you can't get it shipped that way then we might need another option for others to use.
I went back through the document and looked, and ended up with the same choices HighlandReefer posted above. At least for alk, cal, and mag. That's all I'm really trying to get right now. The alkalinity standard he found is 10meq/L. That one is part of a kit being sold separately and I doubt I would have caught that one. :thumbsup: The best other one I could find was 500.
But we're still going to have to cut that down by a factor of three or four before we use it. We need to think about a good way to do that dilution at home and still maintain some accuracy. Maybe using those BD syringes. They're pretty cheap. Not everybody has access to pipettes and volumetric glassware.
The calcium standard is the same way. It's at 1000ppm. But the next lower one is 100. So we're going to have to cut that by at least two preferably three.
The magnesium standard is 1000ppm as well, but that's close enough to the range we're measuring to maybe work. And it's the highest thing they sell. The only problem is that it is in a HNO3 matrix. Yuck. It shouldn't be much of an issue with the kit, but I wish it wasn't in that acid. The calcium standard is in HCl. That's not nearly such a big deal.
We're gonna see how this pans out, but I think the next step is to get some fresh analytical grade EDTA and do this thing myself and try to make something specifically targeted to an aquarium.
I went back through the document and looked, and ended up with the same choices HighlandReefer posted above. At least for alk, cal, and mag. That's all I'm really trying to get right now. The alkalinity standard he found is 10meq/L. That one is part of a kit being sold separately and I doubt I would have caught that one. :thumbsup: The best other one I could find was 500.
But we're still going to have to cut that down by a factor of three or four before we use it. We need to think about a good way to do that dilution at home and still maintain some accuracy. Maybe using those BD syringes. They're pretty cheap. Not everybody has access to pipettes and volumetric glassware.
The calcium standard is the same way. It's at 1000ppm. But the next lower one is 100. So we're going to have to cut that by at least two preferably three.
The magnesium standard is 1000ppm as well, but that's close enough to the range we're measuring to maybe work. And it's the highest thing they sell. The only problem is that it is in a HNO3 matrix. Yuck. It shouldn't be much of an issue with the kit, but I wish it wasn't in that acid. The calcium standard is in HCl. That's not nearly such a big deal.
We're gonna see how this pans out, but I think the next step is to get some fresh analytical grade EDTA and do this thing myself and try to make something specifically targeted to an aquarium.
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disc1
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+1 for the above post.
Thanks for your time and efforts.
Do you really think someone who has spent their life looking for picograms per liter is going to ever be satisfied with something that can't get milligrams per liter right?
This absolutely must be fixed.
HighlandReefer
Team RC
Do you really think someone who has spent their life looking for picograms per liter is going to ever be satisfied with something that can't get milligrams per liter right?
This absolutely must be fixed.
:lol:
:thumbsup:
disc1
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This morning was the RRMAS monthly meeting so I asked some of the members to bring kits for me to play with. We ended up with a couple of API kits. Here's the data we got.
One API alkalinity test was used. This test reads in units of dkH, so using my standard it should get about 9. 9.3 to be exact, but that test doesn't get that level of precision. The result by API was 11dkH. That's not great.
The test was run according to the directions, but was stopped short of the pure yellow end since it went so far over. I stopped the titration once we saw a yellow-green color. It was the first drop that changed us from blue. Had I gone to the pure yellow, I would have got 12 or 13dkH.
Now how many times have I said that the instructions were misleading?
For the calcium test we had two API kits to try. Both kits read 380ppm. The standard should read about 330ppm. So that is a pretty significant error. Both kits required 19 drops, but should have needed 16.
One of the calcium tests went from pink to blue over a single drop. At that point I wondered why people have so much trouble finding an end point with these kits. The second kit answered that question. It was barely colored at all until we got 12 or 13 drops into the test. At 19 drops it turned a bluish purple color. I took this to be the end point. Going further to a true blue with that kit took an additional 3 drops. That would put us way over the expected value. Even stopping at the first appearance of blue (purple in this case) the reading was high by over 15%
While I was at it, I checked the level of the line on the test vial. It wasn't perfect in any case, but was pretty close. I think it's OK to use that line. At least given the lack of accuracy that the rest of the kit made.
The thing I really don't like about the API kit is using the dropper bottle to deliver the titrant. While I am sure that they have created the most consistent drop size they can, any error in the size of that drop will be compounded by the number of drops you use meaning the higher you go the more off you are. The kits that use a syringe to deliver the titrant are going to have a much more accurate and precise measure of how much titrant you used.
Since these weren't my kits and I didn't want to use up a whole bunch of someone else's stuff, I didn't do any precision measurement. We only looked at accuracy over a single run. I did however see enough to know that API is not my favorite kit, based on both the titrant delivery method, and the lack of sharpness in the endpoint.
One API alkalinity test was used. This test reads in units of dkH, so using my standard it should get about 9. 9.3 to be exact, but that test doesn't get that level of precision. The result by API was 11dkH. That's not great.
The test was run according to the directions, but was stopped short of the pure yellow end since it went so far over. I stopped the titration once we saw a yellow-green color. It was the first drop that changed us from blue. Had I gone to the pure yellow, I would have got 12 or 13dkH.
Now how many times have I said that the instructions were misleading?
For the calcium test we had two API kits to try. Both kits read 380ppm. The standard should read about 330ppm. So that is a pretty significant error. Both kits required 19 drops, but should have needed 16.
One of the calcium tests went from pink to blue over a single drop. At that point I wondered why people have so much trouble finding an end point with these kits. The second kit answered that question. It was barely colored at all until we got 12 or 13 drops into the test. At 19 drops it turned a bluish purple color. I took this to be the end point. Going further to a true blue with that kit took an additional 3 drops. That would put us way over the expected value. Even stopping at the first appearance of blue (purple in this case) the reading was high by over 15%
While I was at it, I checked the level of the line on the test vial. It wasn't perfect in any case, but was pretty close. I think it's OK to use that line. At least given the lack of accuracy that the rest of the kit made.
The thing I really don't like about the API kit is using the dropper bottle to deliver the titrant. While I am sure that they have created the most consistent drop size they can, any error in the size of that drop will be compounded by the number of drops you use meaning the higher you go the more off you are. The kits that use a syringe to deliver the titrant are going to have a much more accurate and precise measure of how much titrant you used.
Since these weren't my kits and I didn't want to use up a whole bunch of someone else's stuff, I didn't do any precision measurement. We only looked at accuracy over a single run. I did however see enough to know that API is not my favorite kit, based on both the titrant delivery method, and the lack of sharpness in the endpoint.
HighlandReefer
Team RC
David,
I'm curious if we could just figure the error for a test kit this way and use an Error Factor for a reference for future readings? The amount of error is linear.
N = Error Factor
(Test Kit reading) X N = (Standard used)
(Standard used) / (Test Kit reading) = Error Factor
(Test Kit reading) X Error Factor = The true reading
-------------------------------------------------------------------
When I tried this out with the examples you provided it seemed to work well.
If so, it may be easier for many hobbyists to use this equation to calculate their true readings.
I'm curious if we could just figure the error for a test kit this way and use an Error Factor for a reference for future readings? The amount of error is linear.
N = Error Factor
(Test Kit reading) X N = (Standard used)
(Standard used) / (Test Kit reading) = Error Factor
(Test Kit reading) X Error Factor = The true reading
-------------------------------------------------------------------
When I tried this out with the examples you provided it seemed to work well.
If so, it may be easier for many hobbyists to use this equation to calculate their true readings.
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HighlandReefer
Team RC
Thanks for the update using the API Kits.
"It's listed in the sticky note on articles and links."
Job well done and well deserved.
"It's listed in the sticky note on articles and links."
Job well done and well deserved.
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disc1
-RT * ln(k)
David,
I'm curious if we could just figure the error for a test kit this way and use an Error Factor for a reference for future readings? The amount of error is linear.
N = Error Factor
(Test Kit reading) X N = (Standard used)
(Standard used) / (Test Kit reading) = Error Factor
(Test Kit reading) X Error Factor = The true reading
-------------------------------------------------------------------
When I tried this out with the examples you provided it seemed to work well.
If so, it may be easier for many hobbyists to use this equation to calculate their true readings.
Sure, that's basically the same math. I love it when things are nice and linear. It makes things easy.
I have something going on in the background here that I should probably share. A few months ago Boomer and I helped out with the math for a calculator that TheH was working on for cycling a tank with raw ammonia. I've sent some PM's and I think we are going to get a web based calculator to put this stuff into. I am at least going to put together an excel page that people can download to do it. I know math is a weak spot for lots of people, so I think it would be good to take math out of the equation.
HighlandReefer
Team RC
That's great.
The simpler the better.
The simpler the better.
HighlandReefer
Team RC
David,
Can this be used to check Iodine test kits that detect both iodide and iodate such as the Red Sea & Salifert kits?
http://www.hach.com/potassium-iodide-iodate-standard-solution-0-0125-n-1-l/product?id=7640180319
Potassium Iodide-Iodate Standard Solution, 0.0125 N, 1 L
Natural Sea Water runs around 0.06 ppm total iodine.
Perhaps some hobbyists may be interested in standardizing their kits.
Can this be used to check Iodine test kits that detect both iodide and iodate such as the Red Sea & Salifert kits?
http://www.hach.com/potassium-iodide-iodate-standard-solution-0-0125-n-1-l/product?id=7640180319
Potassium Iodide-Iodate Standard Solution, 0.0125 N, 1 L
Natural Sea Water runs around 0.06 ppm total iodine.
Perhaps some hobbyists may be interested in standardizing their kits.
disc1
-RT * ln(k)
It's a little different with a colorimetric test.
For colorimetric tests we would have to do something different. Using a standard like that would allow you to check up on the kit, but you're still stuck reading a color card. Since the color change might not always be a linear function, we can't always guarantee the same correction factor. And a bit of subjectivity creeps into our measurement.
To really look at a colorimetric test in this much detail, we would need a spectrophotometer to accurately measure the color. Then we could put together a calibration curve.
The other concern I would have with an Iodine test would be the possibility that the error may be different with the different species. What I mean is that you might get two lightly different answers between two samples with the same total iodine concentration but different ratios of iodide to iodate. That's something that would have to be looked into.
For colorimetric tests we would have to do something different. Using a standard like that would allow you to check up on the kit, but you're still stuck reading a color card. Since the color change might not always be a linear function, we can't always guarantee the same correction factor. And a bit of subjectivity creeps into our measurement.
To really look at a colorimetric test in this much detail, we would need a spectrophotometer to accurately measure the color. Then we could put together a calibration curve.
The other concern I would have with an Iodine test would be the possibility that the error may be different with the different species. What I mean is that you might get two lightly different answers between two samples with the same total iodine concentration but different ratios of iodide to iodate. That's something that would have to be looked into.
HighlandReefer
Team RC
Thanks. It's more complicated than I thought.
Yogre
Cheesehead Reefer
The Hanna Checker line are inexpensive colorimetric testers, they're about $50. I have the alkalinity checker. There's a thread going in the Hanna sponsor forum about the Ca checker, some folks are having trouble with it.
I don't have the phosphate or phosphorus checker, but those may be turbidimetric.
I don't have the phosphate or phosphorus checker, but those may be turbidimetric.
disc1
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I've heard real good things about the phosphate tester too.
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