CYA and FC for SWG Pools

[benavidescj]

I am a newbie and am trying to learn about my new pool. I am confused about CYA and FC levels recommended in the Chlorine/CYA chart http://www.troublefreepool.com/pool-school/chlorine_cya_chart_shock/ on this website vs the recommended chemistry for SWG pools http://www.troublefreepool.com/pool-school/water_balance_saltwater_generator also on this website. The recommended levels of CYA and Chlorine for SWG pools is 70 - 80 ppm and 3 -5 ppm respectively. The Chlorine/CYA chart states that the Chlorine levels for CYA levels of 70 - 80 should be 5 - 6 ppm. Which one is correct or am I missing something?

 

[JasonLion]

Welcome to TFP!

Yes, you are missing something. Go back to the Chlorine/CYA chart and scroll down to the second table, which is specifically for SWG pools. SWG pools have different recommended FC levels.

 

[257WbyMag]

Welcome to TFP!

The reason is that our experts have determined that SWCG pools have demonstrated the ability to prevent algae at slightly lower doses of FC at a given CYA level than do manually dosed pools. The chlorine/CYA chart you referenced above is somewhat of a shortened version of this chart...

chlorine-cya-chart-t2346.html

Below the chart, you'll se this footnote which explains the premise...

³Most saltwater chlorine generator (SWG) pools appear to prevent algae at a minimum FC level of 4.5% of the CYA level as compared with the roughly 7.5% of the CYA level shown in the "Min FC" column for manually dosed pools.

I'm am not exactly sure why this is true, but this is what the research and experience of several of our brightest folks here have concluded.

Hope this helps.

 

[benavidescj]

Thanks for the explanation, and it makes sense, but it brings up another question about the tables. I was looking at the right table but the wrong column apparently. I was looking at the "Target FC" column in the SWG table http://www.troublefreepool.com/pool-school/chlorine_cya_chart_shock/ which states that the FC should be 5 ppm for 70 ppm CYA and 6 ppm for 80 ppm CYA. I assumed that this column meant that this is what FC you are shooting for. What does "Target FC" mean? Also, I have read that SWG pools are constatly superchlorinating the pool water as the water passes the cell. Is this the reason why these pools require less chlorine than manual pools?

 

[JasonLion]

The minimum/target wording was originally designed for manual addition of chlorine and might be a little misleading for a SWG. For manual chlorine addition, you add chlorine up to the target level and hope that it is still at the minimum level 24 hours later. A SWG tends to maintain a much more uniform FC level, so the interpretation is slightly different. For SWGs you can think of minimum and target as the two ends of the range you need to be in. Depending on details of your pool you may need to be higher up in the range or you might be able to be lower down in the range.