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The higher end test kits are quite accurate for measuring dKH. The red sea kit I use for example is accurate within 0.14dKH which for all intents and purposes would allow for a margin of error that's not going to harm anything.


That means you have to add 100 drops to measure a dKh of 14.


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That means you have to add 100 drops to measure a dKh of 14.


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Thats actually it's margin of error. Any reading you take with the kit will be between + or - 0.14dKh of the reading you're getting. I.e. if you get a 14dKh reading it will be between 14.14dKh and 13.86dKh
 
Thats actually it's margin of error. Any reading you take with the kit will be between + or - 0.14dKh of the reading you're getting. I.e. if you get a 14dKh reading it will be between 14.14dKh and 13.86dKh


It's too late here.

Is that 0.14 times the reading or +/- the reading?
 
API Alk test kit relies on how good your eyes on colors. Since you count the number of drops (aka 14 drops means 14dkH). I go with Ingy's interpretation of .14 margin of error. Meaning each drop has a graduation of .14. If you have 70 drops then your Alk is 70 x 0.14.
 
API Alk test kit relies on how good your eyes on colors. Since you count the number of drops (aka 14 drops means 14dkH). I go with Ingy's interpretation of .14 margin of error. Meaning each drop has a graduation of .14. If you have 70 drops then your Alk is 70 x 0.14.

I'm not sure what test kit you guys are talking about. I use the red sea test kit where you take 1ml of the solution into a syringe and slowly titrate it into a measured amount of tank water. However much you add when the color changes from blue to orange tells you how much dKh you have. With each drop being roughly 0.01mL 70 drops would put you at 9.8dKh but you don't measure it by drops anyways. I think we are on two different pages here.
 
Isn't that what I exactly said "If you have 70 drops then your Alk is 70 x 0.14."? Which is equals to 9.8 dkH?

Ahh, I gotcha. I thought you were saying that the 70 drops was going to give you a 14 dKh. I must've misread it.

Just for shiggles I measured the volume for drops and 70 drops gives a 10.6 dKh measurement. That's why I said "roughly" 0.01mL / drop. Not that it matters.

However, to get my point across this is straight from the red sea site:
Red Sea said:
Red Sea’s KH/Alkalinity Pro Test Kit is an advanced titration test, measuring the level of buffers in your reef aquarium to an exceptionally high accuracy of 0.05 meq/l (0.14 dKH).

And so we are on the same page; here's the definition of accuracy "The accuracy of a measurement is how close a result comes to the true value."

So assuming that you are measuring a reference solution with a known value of 4dKh you will get somewhere between 3.86 and 4.14 if you take the statement by red sea by its literal meaning.
 
Hmm, that makes sense.

I should change to that when my current test is used up. I use a similar test for calcium and magnesium (I never realized how many drops are in 1 ml). But my Alk test is 1 drop per 1/2 Meq/l.


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Hmm, that makes sense.

I should change to that when my current test is used up. I use a similar test for calcium and magnesium (I never realized how many drops are in 1 ml). But my Alk test is 1 drop per 1/2 Meq/l.


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The red sea kits are great, I got the Reef Foundation kit and it was well worth it. Although the magnesium test is a bit of a pita.
 
Ahh, I gotcha. I thought you were saying that the 70 drops was going to give you a 14 dKh. I must've misread it.



Just for shiggles I measured the volume for drops and 70 drops gives a 10.6 dKh measurement. That's why I said "roughly" 0.01mL / drop. Not that it matters.



However, to get my point across this is straight from the red sea site:





And so we are on the same page; here's the definition of accuracy "The accuracy of a measurement is how close a result comes to the true value."



So assuming that you are measuring a reference solution with a known value of 4dKh you will get somewhere between 3.86 and 4.14 if you take the statement by red sea by its literal meaning.


I think that was what I was curious on as it seems to imply the accuracy isn't constant but improves (as a percentage) as you get higher values.

For example 1.14 (true value 1) is not as accurate as 10.14 (true value 10).

It seems odd?
 
I think that was what I was curious on as it seems to imply the accuracy isn't constant but improves (as a percentage) as you get higher values.

For example 1.14 (true value 1) is not as accurate as 10.14 (true value 10).

It seems odd?


It doesn't matter. The accuracy is always 0.14 +- it is accurate to -+ 0.14 regardless of the true value.

That's the specification of the test kit, Would be interesting to check that though. Be good if it was.

Lol -+ 0.14 per drop...


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It doesn't matter. The accuracy is always 0.14 +- it is accurate to -+ 0.14 regardless of the true value.

That's the specification of the test kit, Would be interesting to check that though. Be good if it was.

Lol -+ 0.14 per drop...


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What Delapool is getting at is that at 1dkh the test kit could be off by as much as 14% while at 10dkh Its only 1.4%
 
What Delapool is getting at is that at 1dkh the test kit could be off by as much as 14% while at 10dkh Its only 1.4%


Yes - that's it.

It's probably pretty irrelevant but I was interested as a lot of our work here depends on (assay) measurements and I've developed a morbid interest.
 
Yes - that's it.

It's probably pretty irrelevant but I was interested as a lot of our work here depends on (assay) measurements and I've developed a morbid interest.


Yeh I get what you mean, I was speaking from a manufacturer perspective when I said it doesn't matter. As long as the reading is within their spec then they are in the clear.

As for the percentage accuracy. I suspect the 0.14dkh accuracy claims will only be valid within a certain range of dkh? Do marine setups typically see low levels of dkh? What would be considered a low dkh in a marine set up?


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Yeh I get what you mean, I was speaking from a manufacturer perspective when I said it doesn't matter. As long as the reading is within their spec then they are in the clear.

As for the percentage accuracy. I suspect the 0.14dkh accuracy claims will only be valid within a certain range of dkh? Do marine setups typically see low levels of dkh? What would be considered a low dkh in a marine set up?


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That information was never supplied so I can't say whether it is or not.

Low dkh would be around 7 and its not really typical to see as the live rock works to buffer and coral will stop absorbing it when it gets low.
 
Did a bit more hunting round today while I was at work. Emailed tech support at red sea.

It must have sounded like I was questioning the accuracy of the kit lol

Here is the response

Thank you for contacting Red Sea.
The accuracy variation quoted of 0.05 meq/l is as you correctly suggest 0.14 dKH, this error factor is added if the dKH is 1.0 or 10 as you suggest, the test kit is designed for use on Sea water aquariums with an optimum dKH range between 8 and 13, the test kit will give you a suitability accurate result in the optimum range.

Whilst the test is easy to perform there are very many factors behind the test that can cause the test to vary, the pH of your aquarium being one of them, this variation would add to the error at a very low range but as stated in the normal range we are confident the test kit works with a high accuracy.

Regards

Kevin Davies
Technical Support Manager
Red Sea Group

So it would seem that there is a range in which the test is more accurate as they are not expecting to typically see a dkh of less than the lower value of their "optimum range"

Hope this helps?


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Did a bit more hunting round today while I was at work. Emailed tech support at red sea.

It must have sounded like I was questioning the accuracy of the kit lol

Here is the response

Thank you for contacting Red Sea.
The accuracy variation quoted of 0.05 meq/l is as you correctly suggest 0.14 dKH, this error factor is added if the dKH is 1.0 or 10 as you suggest, the test kit is designed for use on Sea water aquariums with an optimum dKH range between 8 and 13, the test kit will give you a suitability accurate result in the optimum range.

Whilst the test is easy to perform there are very many factors behind the test that can cause the test to vary, the pH of your aquarium being one of them, this variation would add to the error at a very low range but as stated in the normal range we are confident the test kit works with a high accuracy.

Regards

Kevin Davies
Technical Support Manager
Red Sea Group

So it would seem that there is a range in which the test is more accurate as they are not expecting to typically see a dkh of less than the lower value of their "optimum range"

Hope this helps?


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That's brilliant! Thanks for the post back. Will have to check them out when the API one runs out (some time away though).

Our assays are a little like that. There is the lower assay detection limit (say 0.01% fe). But really we don't get a stable assay reading until something like say 1% fe. The machine isn't really calibrated down that low as only interested in above say 40% fe.
 
That's brilliant! Thanks for the post back. Will have to check them out when the API one runs out (some time away though).

Our assays are a little like that. There is the lower assay detection limit (say 0.01% fe). But really we don't get a stable assay reading until something like say 1% fe. The machine isn't really calibrated down that low as only interested in above say 40% fe.


Yeah I think it depends what you're trying to test. Sometimes readings at a higher level are more unstable and so the tolerance for accuracy becomes a lot wider. Pressure inside an inflated chamber may be one of them where the tolerance is a lot wider at a higher pressure.


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