6/50 = 12%.
8.4/70 = 12%
If you left the production at the same 40%, the FC would climb to 8.4 and then level off.
You would still lose about 3 ppm per day, or slightly less.
Why do SWG need higher CYA?
- Thread starter Amrie
- Start date
8.4/70 = 12%
If you left the production at the same 40%, the FC would climb to 8.4 and then level off.
You would still lose about 3 ppm per day, or slightly less.
- Jul 21, 2013
- 65,429
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Well that is not what happens in real life.
But then real life never matches the theory.
Losses will be "about" the same for the same FC/CYA ratio.
I agree that the real world has too many variables to give an exact answer.
The most important variable is the Hypochlorite Ion concentration, which depends on the FC, CYA, pH etc.
I agree that the real world has too many variables to give an exact answer.
The most important variable is the Hypochlorite Ion concentration, which depends on the FC, CYA, pH etc.
Sure, I get that the swg is only producing based on how long I set it to run. I was trying to ask if they meant there's a linear relationship between FC and CYA that will find itself if the swg variable doesn't change. It sounded like they were saying if you have FC, CYA, and SWG run time balanced to a certain ratio, then you increase CYA and keep SWG run time the same, FC will rise to the very same ratio. Is that correct? Or are there more variables involved, so you'd have to recalibrate run times? Again, I can do these experiments myself (and am), but I'm also curious to have the explanations and understand why.
So after all these (very interesting) side quests, let me see if I understand. TFP recommends keeping higher CYA and FC with a swg because:
the higher levels give a little bigger margin of error for daily maintenance, meaning even if FC drops a little, it may not go entirely out of range and allow water quality to be compromised, which is true for both swg and non-swg pools, but...
since FC fluctuates less dramatically with an swg than manually added chlorine, hopefully you'll have more time to notice and adjust FC before getting to the point of having to shock, and...
since manually added chlorine pools are more likely to go off the rails and need to be SLAMmed (because life happens and the chlorine depends on people remembering to add it), lower CYA in non-swg pools is recommended so that it takes less chlorine to SLAM.
Do I have it so far?
Also CYA levels higher than 50 can help the swg last longer, even though the chart from the CDC suggests benefits top out at 50, because the chart doesn't accurately predict what happens in real world pools. So based on member observations, it seems the total amount of chlorine the swg needs to produce to maintain a given ratio of FC actually keeps decreasing as CYA increases, all the way up to 70 or even 100ppm CYA.
But also, there's nothing inherently different about the chemistry of salt vs non-salt that *requires* higher CYA and FC to sanitize. You *could* maintain any outdoor pool (salt or non-salt) with any of the levels on the chart, just understanding what you're prioritizing: hoping to SLAM less often- or- keeping cost and chlorine consumption down when you do end up needing to SLAM. So TFP made a judgment call and color coded the levels for swg vs non-swg pools, because it practice, it makes sense to prioritize easier SLAMming for non-swg pools. Yes?
the higher levels give a little bigger margin of error for daily maintenance, meaning even if FC drops a little, it may not go entirely out of range and allow water quality to be compromised, which is true for both swg and non-swg pools, but...
since FC fluctuates less dramatically with an swg than manually added chlorine, hopefully you'll have more time to notice and adjust FC before getting to the point of having to shock, and...
since manually added chlorine pools are more likely to go off the rails and need to be SLAMmed (because life happens and the chlorine depends on people remembering to add it), lower CYA in non-swg pools is recommended so that it takes less chlorine to SLAM.
Do I have it so far?
Also CYA levels higher than 50 can help the swg last longer, even though the chart from the CDC suggests benefits top out at 50, because the chart doesn't accurately predict what happens in real world pools. So based on member observations, it seems the total amount of chlorine the swg needs to produce to maintain a given ratio of FC actually keeps decreasing as CYA increases, all the way up to 70 or even 100ppm CYA.
But also, there's nothing inherently different about the chemistry of salt vs non-salt that *requires* higher CYA and FC to sanitize. You *could* maintain any outdoor pool (salt or non-salt) with any of the levels on the chart, just understanding what you're prioritizing: hoping to SLAM less often- or- keeping cost and chlorine consumption down when you do end up needing to SLAM. So TFP made a judgment call and color coded the levels for swg vs non-swg pools, because it practice, it makes sense to prioritize easier SLAMming for non-swg pools. Yes?
Saturn94
Bronze Supporter
- Mar 11, 2015
- 1,864
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- Hayward Aqua Rite (T-15)
Ditto. I notice a significant difference in daily FC loss between 60ppm CYA and 80ppm CYA. If I notice FC loss ticking up unexpectedly, I check CYA. In every case CYA has dropped and once I bump it back up, FC loss returns to normal.