cya: forum vs. manual

[staberg]

hi all,
FC: 3
CC: 0
PH: 7.8
TA: 70
CH: 350
CYA: 40 was wondering what you think about the different recommended levels for CYA. my Pentair manual says 30-50. but TFP says 70-90. any thoughts are appreciated.



17,500 gal; intellichlor IC40; whisperflow 2-speed; CC200 cartridge filter; wet edge Antigua plaster

 

[spidey07]

70-90 is much better for a swg. It won't have to work as much extending its life. The recommendations here are tested tried and true. They frequently conflict with "common knowledge in the pool industry". I trust my trouble free pool to these specs. That's why it stays trouble free.

 

[linen]

I agree with spidey's assessment.

In addition, the cynic in me wonders if the manufacturer does know something about cya effects and wants to sell you a new cell sooner since running at 40 ppm cya will typically mean shorter cell life (more hours sooner) than running at 70-80 ppm cya.

 

[staberg]

thanks for the insight folks...i'll be adding more cya tomorrow. by the way, does anyone remember the ratio for the FC to CYA in percent, I saw it somewhere on this site...from chemgeek perhaps? thanks again

 

[linen]

For a swg you want to maintain a minimum FC level of 4.5% of your cya level. See: http://www.troublefreepool.com/chlorine-cya-chart-t2346.html

 

[chem geek]

but TFP says 70-90

The Recommended Levels for SWG says 70-80 and Water Balance for SWGs says between 70 and 80. Neither says 90.

Most SWG manufacturers say something like 60-80 with 70-80 "ideal" or "best". Pentair seems to be the outlier. The reason for the higher CYA recommendation is that most SWG systems tend to be undersized and would not be able to output enough with the loss of chlorine from sunlight. Even if you purchased an over-sized unit to keep up, the greater SWG output will usually lead to a greater rise in pH, possibly due to both greater aeration from the hydrogen gas bubbles and from undissolved chlorine gas outgassing. Minimizing the SWG output by lowering chlorine loss via higher CYA therefore makes sense.

Though you could go by the 4.5% rule, the Chlorine/CYA Chart is easier to use and a little more conservative (rounding up -- 5% with 4 ppm FC at 80 ppm CYA).

 

[Jeetyet]

Hmmm. The difference in "Recommended Levels" and the implied recommended levels for SWG pools in the "Chlorine/CYA Chart" never registered with me until now. Perhaps the table for SWG pools in the "Chlorine/CYA Chart" should be changed, eliminating the levels for CYA of 60, and leaving just those for 70 & 80. That could eliminate a possible source of some minor confusion.

 

[duraleigh]

Perhaps the table for SWG pools in the "Chlorine/CYA Chart" should be changed, eliminating the levels for CYA of 60, and leaving just those for 70 & 80. That could eliminate a possible source of some minor confusion.

With an accuracy of plus or minus 10 ppm (CYA test) at best, 60-80 works fine for an swg pool. 70 can be considered a "sweet spot" but there are many pools managed successfully by using the 60-80 range.

90 ppm is not a TFP recommendation for all the reasons that have been hashed over here on the forum for years.