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#76
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I don't think we could use Dow Flake. It has a range of percent Calcium chloride which would not be specific enough. We'd need to use a known purity Calcium chloride, anhydrous (or such) chemical.
There are commercial available standards: Hach http://www.hach.com/hc/search.produc...ions+as+CaCO3+(CaCl2),+1000+mg&frasl%3BL,+Bottle&frasl%3B1+L+(NIST) A reliable homemade Calcium standard would require analytical and volumetric equipment, as described here: http://www.athiel.com/lib6/cal.htm Then there are other commercially available Ca standards for different test methods: http://www.chemsupply.com.au/product...earch_type=all The availability and list of what is available is extensive (just Google it!). But, like the article mentions, you want to specify the standard will be used to test Ca test kits used to measure Ca in seawater. We could buy a standard, split it amongst a group and each test using an array of test kits (including duplicate testing of the same test kit). Just a thought! |
#77
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I think it would be prudent to also include the standard the Habib is using for their reference.
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#78
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I've never done such tests because I am not convinced that the results of such tests reflect on the ability of the kit to work in seawater.
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Randy Holmes-Farley |
#79
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#80
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There shouldn't be any unavailabe forms of calcium, unless the sample has solid CaCO3 in it.
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Randy Holmes-Farley |
#81
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Quote:
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Perhaps the Seachem is adjusted to their reference or the reference value is adjusted to their kit or perhaps another scenario? Hard to say. I still have a concern when my LaMotte Test Kit reports X Ca; my Seachem TK reports X Ca; I don't have experience with the Lamotte (and also not with the current Seachem version). However, I explained in my previous post that the Lamotte requires a 12.9 fold dilution with DI water. A slightly premature end-point by 8 ppm will give a 12.9 x 8 = 103 ppm too low value. When we use various standards and also various natural seawater samples (for which the salinities and calcium are known) we get the correct value with the Salifert. Should not a standard, regardless of 'systemic' issues give the expected results? We don't know in what matrix the Seachem "standard" is and also not how the documented value was obtained and what the error in that value is.
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"I'm a big dumb stupid head." - Beerbutt Proud owner of the very rare YET (Yellow Elephantis Tang) from the Lord Bibah Islands. "LOL, well I have no brain apparently. " - dc (Debi) |
#82
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Quote:
__________________
"I'm a big dumb stupid head." - Beerbutt Proud owner of the very rare YET (Yellow Elephantis Tang) from the Lord Bibah Islands. "LOL, well I have no brain apparently. " - dc (Debi) |
#83
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Unless there is inflow of freshwater the calcium value for natural seawater are accurately known as a function of salinity.
Here is a post of a year ago and suggests that the Salifert he used certainly does not give results higher by 25% then actual. Perhaps, in his case, even slightly lower than actual. Quote:
The full thread is there: http://archive.reefcentral.com/forum...li#post3345247
__________________
"I'm a big dumb stupid head." - Beerbutt Proud owner of the very rare YET (Yellow Elephantis Tang) from the Lord Bibah Islands. "LOL, well I have no brain apparently. " - dc (Debi) |
#84
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Quote:
Perhaps the reference might be such but the values for the same marine water sample also don't match. Your post, Mark Middleton's , Leebeca's and a few others made me believe that the 25% or so difference might be systematic.
__________________
"I'm a big dumb stupid head." - Beerbutt Proud owner of the very rare YET (Yellow Elephantis Tang) from the Lord Bibah Islands. "LOL, well I have no brain apparently. " - dc (Debi) |
#85
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But we're not suggesting to test the kit's ability to test seawater. Just the kits ability to do so reliably and accurately. |
#86
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Habib,
The "system issue" is unclear to me. Sorry. Quote:
Isn't this the ability of the operator to find the correct endpoint? and to make the correct dilution? Isn't this reflected in the reproducibility or the precision of the results? If I do multiple tests (e.g., 5 tests), aren't these variables taken into account in the spread of the data/results? How would you eliminate this systemic concern? I appreciate the testimonial, but it's easy to match each one you provide with a counter-testimonial. There are many variables, time, changes in test reagents, was he using kits he bought from a dealer, etc., etc. I'd suggest we stick to the science and clear that up first. Quote:
Does this mean that two test kits may have a systemic problem, but each has a different systemic problem (Seachem because it matches the reference; LaMotte because there's a dilution)? Should we test other kits on the reference and seawater, or if the results are the same, are they also afflicted? I have a Hagen Ca test kit, too. There is no dilution with it; it is a titration test. I'll post my results with it, shortly on the SeaChem reference. Thanks for your input! |
#87
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I performed a Hagen Test (one).
The end point was between 21 and 22 drops. That calculates to approx. 430 ppm Ca. The SeaChem reference is 390 ppm. Last edited by leebca; 08/14/2005 at 08:03 PM. |
#88
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Just checked previous posts. I guess I've done this test before.
The 5. ml mark on the Hagen test tube shows the meniscus touching the bottom of the line with adding 5.00 ml of distilled water, with a Class A vol pipet. If the sample is plus or minus 2 drops (generous) then the sample varies by +- 0.1 ml or 1/50 or 2% The endpoint is readable to the the size of the drop of the dispensing bottle. Using a standard 0.05 ml for that error and it factors 20 ppm into the error of the titration. Add to this the error of the operator determining the endpoint. I don't know if the indicator takes up/uses any of the titrant in their kit. If all were shifted to one end of their ranges, we might be in the neighborhood of about a variation of 30 ppm PLUS the error of determining the endpoint (should be less than a whole drop, maybe 10 ppm). But this 'systemic' variation can be estimated by running multiple test. I don't call this a "systemic" issue, but a precision issue. But then, as I noted above, the use of 'systemic' isn't completely clear to me. |
#89
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Are you basing all of this off only one Salifert kit? Just wondering if perhaps your kit is bad for whatever reason.
I currently use salifert both at my store and at home but used seachem's kits prior to switching. When I checked the kits (both at my store and at home, different kits) against each other I saw no major deviation between the two. That was about a year ago so I don't know the exact numbers. |
#90
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Habib -
I guess I'm on the fence. The only thing I've recently compared my Seachem Ca test was two Salifert kits of similar origin. I've not run another comparison [yet], nor tested the reference recently. I had assumed that my test kit must be `wrong', `old', or `contaminated' when comparing to the Salifert tests - not because I believe the components have changed or the test truly is the above. But when comparing very different #'s, I tried to find some reason and assumed that there was a problem with the kit. If Leebca and any others have similar results - then I think my assumption of a bad kit was incorrect. Maybe my test is more correct than my buddy's Salifert .... now I just don't know. When it was my kit, alone, then I made a guess. Now, I just wonder. And I probably always will, as my kit has all of 15 tests left probably. Provided my Ca doesn't go wildly up/down, in the end I don't really care much if it's 375, 425, or 475. All are fine in my mind.
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read a lot, think for yourself |
#91
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#92
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but wich test kit kit is the closest to being accurate if that is at all possible.Why is it that my saliferts has a 100 ppm differance than my seachem.I just went and tested my friends cal level and got 700 ppm from the salifert test .Is this possible?I did the test twice.I did not test with my seachem as I do with when I test my water.I don't understand why the 100 ppm dif between the two..I try to take the air bubbles out and I always follow directions to make sure that no mistakes are made.I tested my water salifert 560 ppm seachem 465 ppm.Could it be the ro water causes the kit to test low?Very frustrating
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silicone can be deadly! |
#93
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With the Seachem kit you should be using DI water (TDS = 0). Your RO water could be causing an inaccurate reading.
700 ppm is very unlikely - if even possible. I've only heard of those kind of numbers from people using Oceanic salt. |
#94
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Hobster:
For that Salifert batch when retesting today an archived sample I found when using a commercial calcium in freshwater standard 425 mg/L (should have been 434 mg/L). Using a natural seawater with a salinity of 36.5 S I found 435 mg/L (should have been 440 mg/L). The archived sample of that batch performed very good. Details can be found here below. 1] Used a commercial standard see attachment at end of this post having a specified batch analysis of 1001 +/- 2 mg/L and a density of 1.01 kg/L. Took 0.876 g which equals to 0.867 ml (weight / density). The Salifert method is based on a sample of 2 ml so the expected calcium value is: 0.867 / 2 * 1001 = 434 mg/L Found using your batch 425 mg/L. 2] Used a natural seawater collected off the coast of Lanzarote, a few hundred miles to the west of the Sahara and no inflow of freshwater). Salinity 36.5 S. Natural sewater with a salinity of 35S has a calcium concentration of 413 mg/Kg = 423 mg/L. A natural seawater with a salinity of 36.5 should have 440 mg/L calcium. Used 2 ml of the NSW with a salinity of 36.5 and also weighed as a double check the 2 ml sample and found to be 2.044 g. That sample gave a value of 435 mg/L. Quote:
__________________
"I'm a big dumb stupid head." - Beerbutt Proud owner of the very rare YET (Yellow Elephantis Tang) from the Lord Bibah Islands. "LOL, well I have no brain apparently. " - dc (Debi) |
#95
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If it was Alkalinity ... I'd be much more concerned.
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read a lot, think for yourself |
#96
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Habib, Thank you for checking that batch number. So based on these results the kit is accurate to +/- 5-9 mg/l ?? Works for me! Closer than I will ever measure Thanks.
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"You call someplace paradise, kiss it goodbye" The Last Resort, The Eagles |
#97
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Re: Salifert v. Seachem Ca Test Results
Quote:
Leebeca, which brand of salt did you test which gave 250 ppm with the Seachem and 350 ppm with the Salifert? TIA
__________________
"I'm a big dumb stupid head." - Beerbutt Proud owner of the very rare YET (Yellow Elephantis Tang) from the Lord Bibah Islands. "LOL, well I have no brain apparently. " - dc (Debi) |
#98
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Habib,
Red Sea. |
#99
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Red Sea , IIRC, also claims it to have that value. I'll check that salt also with another lab grade kit.
__________________
"I'm a big dumb stupid head." - Beerbutt Proud owner of the very rare YET (Yellow Elephantis Tang) from the Lord Bibah Islands. "LOL, well I have no brain apparently. " - dc (Debi) |
#100
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RichardS & MiddletonMark
I disagree. I care if my Ca is 375 or 475 when managing pH lowering effects on my system. I'd boost the 375 and maintain high alk to make sure that at the lower pH my specimens have easy access to as much Ca as they need. |
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