Hot Tub Forum

Original => Hot Tub Forum => Topic started by: 999 on May 18, 2012, 11:38:34 am

Title: How do you calculate how much Cyanuaric Acid is in your tub
Post by: 999 on May 18, 2012, 11:38:34 am

I am about to do a water change after 3 months using dichlor and MPS shock.

I know how many tea spoons of 55% dichlor that i have used in that time but don't know how many ppm  that is.

I do know that for every 10ppm of dichlor I am adding 9 ppm of CYA..

Is there a standard measure of what 1 teaspoon of dichlor in a 1700 litre tub relates to in dichlor ppm.

Title: Re: How do you calculate how much Cyanuaric Acid is in your tub
Post by: chem geek on May 18, 2012, 05:21:16 pm

You can use The Pool Calculator (http://www.thepoolcalculator.com/) by changing the units to "Metric", entering 1700 liters for the volume, going down to the bottom of the page to "Effects of adding chemicals" and selecting "dichlor" from the pull-down menu, and entering the number of grams you have added which is the number of teaspoons times 4.725 so 1 teaspoon (4.725 g) raises the FC by 1.5 ppm and the CYA by 1.4 ppm.

Note that there is a loss of CYA over time as chlorine slowly oxidizes it so figure losing around 5 ppm CYA per month.

Title: Re: How do you calculate how much Cyanuaric Acid is in your tub
Post by: 999 on May 19, 2012, 05:49:01 am

chem geek.. thats just what I was looking for, thanks.

In the last three months I have added 116 tea spoons of 55% Chlorine granules. That equates to 548 g. The calculator shows that my CYA will be at 163. Taking into account a loss of 5 ppm per month, then it will be around 148. I think I am right in saying that anything over 100 is too high, so although the water looks fine I will be changing it today after 101 days.

I have been shocking with MPS, but I have recently done a dichlor shock so that has added to the CYA in recent weeks.

(just by using your estimate of 1 teaspoon of dichor adds 1.4 ppm of CYA also equates to 162.4 ppm (116x1.4) so that is a good guide for me)

Title: Re: How do you calculate how much Cyanuaric Acid is in your tub
Post by: chem geek on May 19, 2012, 07:47:56 am

You can always compensate for a high CYA by having a higher FC level, but you are right that at some point that becomes impractical and what usually happens with Dichlor-only users is that the water starts to turn dull which is most noticeable after a water change when the water becomes so noticeably fresh and clear.  With users who manage their CYA level (say, Dichlor-then-bleach), the water stays in good shape longer and after a water change the difference is less noticeable because the water didn't get as dull/cloudy because the active chlorine level is more consistent so keeps up with oxidizing bather waste better.