Chemistry of the CYA test from TFTESTKIT

michiele

LifeTime Supporter
May 18, 2007
24
Broken Arrow, OK
#1
I received my TFTESTKIT today. I am so excited to test everything. I just did the CYA test. I was just wondering what is the chemistry behind this test. What makes the solution turn cloudy? Is it cloudy as it comes out of the mixing bottle? Since my CYA is so low, I didn't get much cloudiness until around the 20ppm line. (I know that is right though since we just filled the pool in the fall. The only chlorine that has been put in was a once a month dichlor and then I shocked at opening with calcium hypochlorite.) I was just curious how this test actually works. Thanks.
 

CaOCl2

LifeTime Supporter
May 23, 2007
326
Montreal Canada
#2
What you're doing in that test is adding a measured amount of melamine to the water sample that precipitates the stabilizer. The amount of turbidity produced is not linear but follows Lambert Beer's Law. It can be measured by different "methodologies", dissappearance of an indicator dot (inside a graduated cylinder or at the end of a graduated stick), or through a photometer.
 

JohnT

Admin
Mod Squad
TFP Expert
Apr 4, 2007
9,460
SW Indiana
#3
The CYA reagent is melamine, and it reacts with CYA to form crystals in the solution that increase the turbidity of the water. This is the same mechanism that the tainted pet food involved, and the crystals caused clogging in the kidneys.
 

michiele

LifeTime Supporter
May 18, 2007
24
Broken Arrow, OK
#4
CYA

Thanks for the replies. I have always been interested in Chemistry so it helps me to understand the tests better. I considered a Chemical Engineering degree back in school for about a year, until I took Organic Chemistry. Suddenly, I just didn't get it anymore:) I changed to a Mathematics degree! But since that was almost 20 years ago, I don't remember much about that either:)
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
#5
Take a look at this link on Wikipedia for Melamine where they also show the Melamine cyanurate precipitate. It is sold as a solid for use as a flame retardant. If you look up melamine cyanurate solubility, you will find links like this one that list 0.001g/100ml which is 10 ppm or www.wdchem.com/pages/p6-e.html+melamine+cyanurate+solubility&hl=en&ct=clnk&cd=18&gl=us&client=firefox-a]this one[/url] that lists 0.002g/100ml which is 20 ppm. So I wrote to Taylor Technologies (a while ago) about how their test can measure down to 20 ppm (in the K-1720 test kit) and they wrote back saying that the solubility measurements are at a standard pH of 7.0 while the melamine solution they provide is quite acidic and that melamine cyanurate is essentially insoluble at low pH.