CYA in a sock

[waterbear]

Precursor: http://www.poolforum.com/pf2/showthr...4969#post64969

CYA Application Experiment June 29, 2010

Though I was fully prepared to retract my rash assessment before doing this experiment (and may still have to if my pool turns out to be 9 or 10K gallons instead of the 14K gallons I believe it is) it appears that I have been conservative in my estimation that CYA dosing shows up in testing in a few hours instead of a few days. I think preliminary testing shows that there is nearly full dissolution in less than 60 minutes.

Procedure

Using the Pool Calculator, 37 ounces (wt) of cyanuric acid (stabilizer) should increase CYA by 20 PPM and effect a reduction in pH of .37

Predict CYA 50 PPM and pH 7.33

I weighed the CYA granules on a postal scale and split into two batches, making a one gallon slurry from each and adding one right after the other into the skimmer (basket in place). Granules disappeared from both skimmer basket and pump basket in about 6 minutes. Water samples were drawn from the same location in the pool (midway between shallow and deep end) and about 18 inches from the surface. I used a 44 mL sample and 5 drops R-0004 phenol red indicator titrant for the pH test; and a 15 mL sample tube (7 mL sample and 7 mL cyanuric acid reagent) for the CYA test. All sample tubes and collectors were rinsed before testing with sample water and afterward with tap water. The CYA samples were each shaken for 20-30 seconds and titrated into a 9 mL view tube immediately. The temperature of collected sample water was 89° F . At no time was I wearing socks. 

Test Results

BEFORE ADDITION
pH 7.7
CYA 30 PPM

AFTER ADDITION
15 minutes
pH 7.5
CYA 40 PPM

30 minutes
pH 7.4
CYA 45 PPM

60 minutes
pH 7.4
CYA 50 PPM

120 minutes [pending]
pH - - -
CYA - - - PPM

24 hours [pending]
pH - - -
CYA - - - PPM

I’ll edit this post to update the last two entries as they become available.

Questions? Scoffs? Rebukes?

I have performed similar experiments and it has taken about 36 hours with pump running for the full amount to show in the best test I had. Then again I was not testing evey hour since it's a waste of reagent, IMHO

Also, by my calculations it should take 37.3 oz of CYA to raise 14k gallon by 20 ppm (and I don't use the pool calculator) so we agree there. Have you verified that your pool is 14k?(There is a way to chemically determine the gallonage of the pool using a modification of the Taylor TA titration to give you a result of 1 ppm and baking soda if you are interested) If not then the experiment should be carried out with testing for a few days until the CYA no longer rises to make sure you have reached the endpoint of your experiment
.
Also the water flow has a lot to do with how quickly it dissolves so this is definitely a case of YMMV. FWIW, when i have used a skimmer sock and put the CYA in that it stayed in the sock for a few hours before there were no traces left. Also, water temp will play a small part here since CYA is very slightly more soluble in hot water(but again, the difference is slight.)
Also, as anyone who has ever broadcast CYA in the pool can attest to, it stays on the bottom for around 6 hours before it seems to disappear. Once again, I believe the water flow, or lack thereof, plays a factor here.
There are really just too many variables which is why it is safe to say retest in a week. This ensures that the CYA has dissolved and that you are not wasting reagent (although those that sell test kits often want you to waste reagents and have to buy refills).


I always told my customers to add it, wait a week and then retest but I always assumed that they were getting at least some protection from UV by the next day.

What I don't get is those that are so afraid of CYA that they add such small quantities for the size of their pool that are barely measurable and wonder why it does not seem to rise. If you overshoot the CYA by 10 ppm it is not the end of the world and probably will have no impact on how you have to care for your pool (Even if you miss the magic number of 50 ppm and end up at 60!) The test is subjective at best so we are really only ballparking it anyway.