Just curious and my chemistry is limited - one probably for Chemgeek. Does all the CYA get converted to melamine cyanurate in the precipitation test, and does that crystal formation 100% remove free cyanurate ions in solution?
Melamine - Cyanuric Acid reaction
- Thread starter mikech
- Start date
The short answer is yes. However, there are details (of course). In neutral pH water, melamine cyanurate is soluble to around 20 ppm or 30 ppm (sources vary on this) and the main reason is that at neutral pH most of the cyanuric acid is singly charged cyanurate ion so the hydrogen bonding (which is a weak bond) of CYA to melamine has to overcome an equilibrium reaction of CYA and cyanurate ion.
The way the Taylor CYA test kit overcomes this is to use a low pH buffer in the melamine reagent. That forces nearly all the CYA to be actual cyanuric acid that will form a precipitate with melamine.
If there is chlorine in the water sample, then the chlorinated cyanurates similarly can interfere with the formation of melamine cyanurate where the worst case would be that the CYA level reads too low by the amount of FC. This can be easily overcome by adding a chlorine neutralizer to the water sample, such as a few drops of R-0007 reagent.
The way the Taylor CYA test kit overcomes this is to use a low pH buffer in the melamine reagent. That forces nearly all the CYA to be actual cyanuric acid that will form a precipitate with melamine.
If there is chlorine in the water sample, then the chlorinated cyanurates similarly can interfere with the formation of melamine cyanurate where the worst case would be that the CYA level reads too low by the amount of FC. This can be easily overcome by adding a chlorine neutralizer to the water sample, such as a few drops of R-0007 reagent.
Mmm, thanks for that. I was having a wacky idea about if it was possible to develop a modified TA test to measure the difference in TA caused by the cyanurate ions being taken out of the equation in affecting TA. At pH 8 the correction factor is .36 caused by CYA, so at high CYA's I thought it might be measurable, leading to a drop based CYA test. Raising the pH to 8 would negate the buffer so that screws it!
As an aside, I've subsequently seen TA correction figures for 30-50ppm CYA at various pH values. I assume this breaks down at high CYA levels otherwise members would be reporting proportionately high TA's and this doesn't seem to be the case. Why is that?
Thanks again, Mike
As an aside, I've subsequently seen TA correction figures for 30-50ppm CYA at various pH values. I assume this breaks down at high CYA levels otherwise members would be reporting proportionately high TA's and this doesn't seem to be the case. Why is that?
Thanks again, Mike
The problem is that you don't have an easy way of measuring carbonate alkalinity by itself so that you could subtract that from TA to get an implied CYA level at a certain pH.
PoolMath has the exact formula (or a lookup table for it) for the CYA factor at various pH. Basically there is a chemical equilibrium between CYA and cyanurate ion that is a function of pH. Cyanurate ion measures as TA in the TA test so needs to be subtracted out to calculate the calcite saturation index that depends on the carbonate alkalinity. The borates also contribute to TA (though not that much) and again PoolMath takes care of all this automatically for you.
The CYA contribution to alkalinity does NOT break down at higher CYA level. At very high CYA levels you will see higher TA levels. If you don't, then the carbonate alkalinity is very low, but it shouldn't be lower than the carbon dioxide level in air. So the following shows the minimum TA level for each CYA level all at a pH of 7.5 assuming that carbonate alkalinity is 11 ppm.
CYA ... Min.TA
. 30 ....... 21
. 50 ....... 27
100 ....... 43
200 ....... 75
300 ..... 107
500 ..... 171
You can see that it would take very high CYA levels before you'd notice something that didn't make sense such as a TA level that was too low. In practice because carbonate alkalinity is not that low, you see TA numbers higher than the above. However, pools with high CYA usually use Trichlor so their carbonate alkalinity may be low if not restored, though usually pH Up is used and that tends to keep carbonate alkalinity on the high side.
PoolMath has the exact formula (or a lookup table for it) for the CYA factor at various pH. Basically there is a chemical equilibrium between CYA and cyanurate ion that is a function of pH. Cyanurate ion measures as TA in the TA test so needs to be subtracted out to calculate the calcite saturation index that depends on the carbonate alkalinity. The borates also contribute to TA (though not that much) and again PoolMath takes care of all this automatically for you.
The CYA contribution to alkalinity does NOT break down at higher CYA level. At very high CYA levels you will see higher TA levels. If you don't, then the carbonate alkalinity is very low, but it shouldn't be lower than the carbon dioxide level in air. So the following shows the minimum TA level for each CYA level all at a pH of 7.5 assuming that carbonate alkalinity is 11 ppm.
CYA ... Min.TA
. 30 ....... 21
. 50 ....... 27
100 ....... 43
200 ....... 75
300 ..... 107
500 ..... 171
You can see that it would take very high CYA levels before you'd notice something that didn't make sense such as a TA level that was too low. In practice because carbonate alkalinity is not that low, you see TA numbers higher than the above. However, pools with high CYA usually use Trichlor so their carbonate alkalinity may be low if not restored, though usually pH Up is used and that tends to keep carbonate alkalinity on the high side.
Really, really appreciate the reply. There should be a better badge than TFP Expert, may be The Enlightening One! 
so I should be adding some 007 to my first 7 ml of pool water before I add the 013 to complete the CYA test?
If your FC is particularly high, say at SLAM levels or above 10 ppm, then it would be a good idea. If it's at normal FC levels, it wouldn't hurt but I'd say you could try it both ways and see if you notice any difference. We haven't done experiments to see exactly how much of an effect it has -- there does appear to be one but we don't know how much (i.e. is it the full amount of FC lowering the CYA level by that amount or is it less than that).
In 7 ml of pool water, you should only need one drop of R-0007 since one normally adds only a couple of drops in the TA test that is larger in volume.
In 7 ml of pool water, you should only need one drop of R-0007 since one normally adds only a couple of drops in the TA test that is larger in volume.