Question about CYA and FC

[93mastercraft]

I have my water tested reqularly by a local pool dealer, because that's where I baught the pool. But this season I decided to go full blown BBB. But while I had some Chlorinating tablets(stabilized) left over and decided to use them. Well, my CYA has risen to 100PPM and my FC is 11.5 and my TC is 13.5. From looking at the CYA/FC chart, I should be about right, right???

The "professionals" at the pool dealer seem to think my FC & TC is too high. I tried explaining the effects of CYA and the effectiveness of chlorine. Well. the professionals are telling me that the CYA only effects how fast the chlorine gets "burned off" in the sun and my chlorine levels are too dangerously high to swim in. So, help me out here, I'm getting confused.

 

[TravisD]

My first bit of advice would be to get a good test kit and start testing yourself instead of listening to the pool store. I had a similar experience last year and was told the same thing by the pool store. "FC too high, it should only be 1 ppm"
Bottom line is that there is plenty of documentation that states the total opposite of what the pool store has told both of us.
I got some great responses in my thread from last year and I think if you read some of it, it would certainly clear things up for you.
Also, I would recommend getting that CYA level down to a more manageable level. Somewhere in the neighborhood of 40 - 50.
You can look at my thread here.
Hope this helps you out.

 

[chem geek]

(I wrote this as TravisD was posting)

The "professionals" at the pool dealer are wrong. If they remember any chemistry at all, then show them this paper. They can also look at the "Chlorine / CYA Relationship" section (and its links) in this post.

In your situation with an FC of 11.5 and a CYA of 100 ppm, assuming a pH of 7.5 (and temperature of 77ºF), 99.09% of the measured FC is bound to CYA (in a series of compounds called chlorinated isocyanurates) and has very little reactivity (i.e. does not kill pathogens nor kill/inhibit algae nor oxidize bather waste to any reasonable degree) and virtually no skin absorption nor volatility. 0.44% of the FC is hypochlorous acid while 0.47% is hypochlorite ion. This amount of hypochlorous acid and hypochlorite ion is the same as would be found in a pool with 0.10 ppm FC with no CYA. The only issue with the high FC would be if you were to drink/ingest the water in large quantities.

Even the ANSI/APSP-11 standard in section "A8.3 Cyanuric Acid" states the following:

However the affinity of chlorine for cyanuric acid is strong enough that most of the “Free Available Chlorine” at any given point in time is bonded to cyanurate and the hypochlorous acid concentration is only a fraction of what a free available chlorine test and pH would indicate. [...] Lowering the hypochlorous acid concentration can have a significant impact on the rates of any reaction for which hypochlorous acid is involved in a rate limiting step. Specifically disinfection and oxidation of contaminants can be slowed by the lowered hypochlorous acid concentration.

Unfortunately, the standard does not state explicitly how much chlorine is in fact bound to CYA though that can be tediously calculated using the equilibrium constants in the paper I linked to above. I have a spreadsheet here that does these tedious calculations.

Richard

 

[93mastercraft]

Thanks for all the fine responses and additional information! I'd much rather read about and learn from those who back up their comments with proof, instead of taking someone's word for it. But then again, the pool dealer asked me if I believe everything I read on the Internet...LOL! I work in IT and the Internet has kept me in a job for 15 years now and I have a clean, crystal clear safe private pool to show for it and swim in it.

 

[bk406]

And I had a pool guy tell me one time that adding fresh water to the pool dilutes the salt concentration. I told him that was true except if the water loss was from evaporation. He then proceeded to tell me that it was the same. I asked him where the salt went, and he said it evaporated with the water


So dont believe much of anything a so called "pool guy" tells you in a lot of cases

 

[teapot]

I asked him where the salt went, and he said it evaporated with the water

I wonder if that twit knows how commercial salt producers would ever make anything if their salt evaporated, so the Bonneville salt flats don't exist. Priceless, you have made my day :lol: :lol: :lol:

 

[frustratedpoolmom]

Your CC is 2, according to your posted numbers- anything above .5 you need to shock the pool.

You'll have a much easier go of it, if you drain 50% of your pool water to lower the CYA level down - you'll need much less bleach/chlorine to accomplish this task.

Read How to Shock your Pool in Pool School.

 

[Butterfly]

Your CC is 2, according to your posted numbers- anything above .5 you need to shock the pool.

You'll have a much easier go of it, if you drain 50% of your pool water to lower the CYA level down - you'll need much less bleach/chlorine to accomplish this task.

Read How to Shock your Pool in Pool School.

I agree with fpm. Also, most CYA testers are able to test to 100, so it could be higher.