Cyanuric Acid Solubility

rock

Well-known member
Apr 26, 2012
263
TomU said:
Do you think another 100 degrees will make a noticeable difference?
This paper says the pH will make a greater difference in solubility:
http://jspsi.poolhelp.com/ARTICLES/JSPS ... p09-16.pdf

And, this MSDS gives the solubility of CYA as 2,000 mg/l@ 25ºC
http://www.sciencelab.com/msds.php?msdsId=9923614

Wikipedia puts the solubility of CYA in water at 2,700 mg/l@25ºC

Roughly converting to American units, 1 pound of CYA will dissolve in 50 gallons of water at 25ºC at saturation levels.
It would be interesting to see what the saturation numbers are for 100ºC.
 

rock

Well-known member
Apr 26, 2012
263
Re: Faster Dissolving Cyanuric Acid

kenmar said:
Why can't I just put the CYA chrystals in a 5 gal bucket of water, let it sit for a week, and then add it to my pool?
I suspect, that, after a week, all the cynauric acid that could dissolve in that 5 gallons of water WILL dissolve into that 5 gallons of water.

So we need to calculate how much 'can' dissolve in 5 gallons of water.

This MSDS gives the solubility of CYA as 2,000 mg/l@ 25ºC
http://www.sciencelab.com/msds.php?msdsId=9923614

And, Wikipedia puts the solubility of CYA in water at 2,700 mg/l@25ºC

Roughly converting to American units, 1/10 pound of CYA will dissolve in 5 gallons of water at 25ºC at saturation levels.

So, if my math is right, you can stick as much CYA as you want in the 5-gallon bucket ... but only 1/10 of a pound can possibly dissolve.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
The CYA is not slow to dissolve because it is getting anywhere near saturation. It is slow to dissolve because of the amount of energy it takes for water to dislodge a CYA molecule from its crystal structure (analogous to an activation energy for chemical reactions). The rate of dissolving is going to have a far greater dependence on the surface area of the granules and on the circulation of water around them. If the CYA were more finely crushed, it would dissolve more quickly, though might be so light that it wouldn't readily break the surface tension of water and might float on top. We see this for some finely powdered boric acid, for example.

I have always added CYA into a T-shirt in my skimmer with the pump running and it visibly dissolves completely within 24 hours and I usually measure at least 80% of the expected CYA level the next day meaning that it has mostly chemically dissolved as well. Note that if I had put it in the skimmer without the T-shirt, it would take much longer to dissolve since the water velocity through the filter is very, very slow. When my pump is at 48 GPM, the skimmer might be at 15 GPM with a water velocity over it's 6" diameter of 0.17 feet per second or 2 inches per second. My 340 square foot cartridge filter only has an average water velocity through it of 0.0038 inches per second (0.1 millimeter per second) so you can understand why it takes so long for CYA to dissolve in filters.
 

rock

Well-known member
Apr 26, 2012
263
chem geek said:
It is slow to dissolve because of the amount of energy it takes
Hi ChemGeek,
That is very interesting! I took organic and inorganic chemistry in college (many decades ago), and I don't remember this practical stuff at all! It's amazing that we don't learn the good stuff (like this) until we do and think about what it is we do!

chem geek said:
I have always added CYA into a T-shirt in my skimmer with the pump running
I ask this question only because 'my' skimmers are not filtered - and - worse yet - my skimmers feed little orifices in the pop-up cleaning system.
Q: Would you recommend skimmer feeding for a self-cleaning pool (i.e., unfiltered skimmers).

Seems to me 'we' self-cleaning people might want to consider putting the t-shirt in the debris canister 'if' having the pieces that slip through stick to the filter until dissolved is critical in the equation.
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,880
Silver Spring, MD
Since your skimmer doesn't lead to your filter, you do not want to pour granular CYA into the skimmer. However putting CYA in a sock in the skimmer would be fine.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
Also note that my skimmer has a bypass (equalizer) into the pool and I also have two floor drains so even if the skimmer gets blocked with the CYA it doesn't cause any problems with the pump. You wouldn't want to put CYA in something that blocked the skimmer if there were not other ways for water to flow to the pump.