Taylor CH, Salt tests and Magnesium Chloride

mgtfp

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Mar 5, 2020
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That's quite interesting, I like the idea of this Red Sea CH test. Looks more fiddly, but it also offers a 5ppm accuracy. Seems to cost about 65AUD for 75 tests. That's actually alright. The CCL test gives me 70 tests with 25ppm accuracy for 40AUD. You could probably reduce the sample size from 5ml to 2.5ml and get 150 tests out of the Red Sea kit with 10ppm accuracy (5ppm might be required for fish, but 10ppm should definitely be enough for a pool). I also like the idea of the more quantitative titration, not having to rely on reproducible drop size. And you won't have a problem with Mg contamination (which I don't think I have, but who knows what the previous house owner has put into the pool...).

I saw that Red Sea also offers a test to measure Carbonate Alkalinity (CA), not Total Alkalinity (TA). I was wondering if that could offer an indirect method to test for CYA. If you tested both, CA and TA, and know your FC and pH, then you should be able to calculate CYA by using chemgeek's Pool Equations. When using the simplified formula for CA that's behind PoolMath, then you wouldn't even need FC and pH. I would love to get rid of the dreaded black-dot test and replace it with a quantifiable titration.
 
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JoyfulNoise

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May 23, 2015
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Their carbonate alkalinity test is basically the same test as the Taylor test. When CYA and bicarbonate are both present, they add to there alkalinity over the same pH range and so you get a Total of the two. If you were to use the Red Sea dKH test, you'd get the same value as the Taylor TA test. The Red Sea test can't distinguish CYA from bicarbonate. In a reef tank, one would only expect carbonate and bicarbonate alkalinity with a pH roughly above 8.2 . Thus you first titrate the carbonate alkalinity using phenolphthalein indicator and then you add methyl orange or another suitable mixed indicator (like the Taylor indicator) and you then titrate all of the bicarbonate alkalinity. Depending on the volumes and normality of the titrant used, there are simple formulas to determine the concentrations of carbonate and bicarbonate. One would never find cyanuric acid in a reef tank, nor any other significant alkaline species (such as borates or phosphates...although once could correct for phosphates as it would build up from large concentrations of spent food or metabolic waste).
 

mgtfp

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Mar 5, 2020
730
Melbourne, Australia
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Chlorine
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Astral VX 7T
Thanks for the explanation, Matt. That makes sense. If you don't expect any CYA or other TA contributers in your fish tank, just call your TA test a CA test, and don't confuse aquarium owners that will probably never have heard about CYA.

Would have been too good to be true...