CYA question

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Kurtomac

Well-known member
Nov 18, 2019
73
Maryville, TN
Curious why a 70-80 cya is recommended for a SWCG pool versus a 30-50 for a traditional chlorine pool? Is it because a lot of SWCG or too small for the pool size and they need the extra chlorine loss protection or what? I have my CYA right now and have been maintaining 4-5 FC level. I picked up some stabilizer the other day but haven’t added it yet. As the heat approaches and usage will increase I was preparing to increase the cya to 70 but got to thinking so here I am. Why would I want to have to run a FC of 7-8 (10% of cya) when when I could run a 4-5 at my current cya? I have 3 young children and the less chlorine exposure the better was my thinking. I have my RJ 60+ at 20% for 12 hrs a day right now (I kind of went over kill one the SWCG so it can keep up when demand is high). Pool looks great and have been doing weekly testing. My PH is stable at 7.8 and TA is 70.

Btw I picked up a speed stir and that thing is awesome. I feel like I’m gettin more accurate readings as sometimes when I think the color is changing it goes back and requires just one last drop

I guess I’m a little CYA gun shy after last year being my first year owning a pool using shock shock that made my CYA 150+ and then draining a ton to get back to normal. Then started off the season this year changing to VS and SWCG and following the advice of this forum and thus far this season life has been great. After many hours of reading I have a much better understanding of what I’m adding and the chemistry
 
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Two things you haven't considered:

1) Stabilizer buffers Chlorine. One way of thinking (not entirely accurate, but good enough for illustration purposes) about this is that it lowers the "perceived level" of chlorine in the pool. I have typically (prior to getting a SWG) run my pool at 40 CYA, which means I have a target FC of 5-7, and a SLAM level of 16. We have swam in it countless times with an FC of 7 or more (and even at 16), with no sting in the eyes or fading of our swimsuits. But then we go to a water park for an hour or two where FC is 1 or 1.5 with a CYA of zero, where your eyes feel like someone hit them with a blowtorch and you can literally watch the fabric fade in real-time.

2) SWG-managed pools have lower FC requirements per CYA than LC-managed pools. You can see the chart here: Chlorine / CYA Chart - Trouble Free Pool If you raise your CYA to 70, your target FC is exactly the 5ppm you have it at now. The difference is, you won't have to run your pump and/or SWG as much, so you save money on electricity, and your cell lasts longer before it needs to be replaced.
 
If chlorine is there for sanitizing and to fight off organics then I guess I’m still confused as to why the target FC is lower at a given CYA for a salt pool vs regular.

I’m not here to argue...just to understand better. I’ll be raising to 70 and shooting for FC of 5 in the next week.

My pump only runs 14 hours a day and swcg 12 hours a day at 20% so currently it doesn’t have to work very hard. But it’s not been overly hot and the swim load is light. Also the new VS pump is only costing me at or less than $15 a month so I’m not concerned about run time like I was with my old single speed
 
Because SWGs will constantly produce chlorine they are able to better maintain the FC level. If you are manually adding LC you are likely just doing it once a day, or maybe even once every couple of days and the FC level can swing much more. By using the SWG to keep the FC level more stable you can get by with a lower FC level.
 
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Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...
www.troublefreepool.com www.troublefreepool.com

A very deep read, but within it is the scientific reason for the higher CYA level for SWCG. The lower minimum FC /CYA ratio for SWCG pools is due to the extended time frame of addition and less up and down FC levels in the water column. The buffer can be lessened because of this.
 
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Many of the recommendations we have come out of thousands of reports on how pools react at certain levels. If you compare our recommendations, not only is the CYA higher for a SWCG pool, the FC level is slightly lower. Again, thousands of reports have shown that a slightly lower level of FC is fine in these pools. Probably as Marty points out because there is a more constant level of FC in the pool with a SWCG.

As to less FC being better for the kids, it all comes down to percentages in the CYA/FC ratio. 7% FC ot CYA is the same if FC is at 2 or at 20 (which is where I needed to keep mine when my CYA was 250+). You always have to take the buffering effect of higher CYA on FC when you think about the effects it has on swimmers.
 
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tim5055 said:
Many of the recommendations we have come out of thousands of reports on how pools react at certain levels. If you compare our recomendations, not only is the CYA hiogher for a SWCG pool, the FC level is slightly lower. Again, thousands of reports have shown that a slightly lower level of FC is fine in these pools.
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And this is why I’m going to go ahead with it. Was just trying to understand it. I get that my pool is being fed chlorine regularly throughout each and every day rather than relying on spikes in levels when adding LC and having to keep it high enough to make sure it doesn’t drop too low before the next addition.
 
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I had a mess of a year last year with algae blooms but I understand why. Hoping I go the whole season without an issue. Weekly testing and cleaning and maintaining my FC of 5 and hope all goes smooth! Now I kind of want to add a heater haha. Wish I would have thought of this before I redid all my above ground plumbing this year with the new pump and swcg
 
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Kurtomac said:
Weekly testing and cleaning and maintaining my FC of 5 and hope all goes smooth!
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We find that most test a little more often than weekly. At first it will be almost daily until you get the SWCG dialed in. Even then differing weather patterns will effect the level of Fc in the water. A cloudy rainy week may see your FC go up as the UV burns off less and the SWCG produces the same amount of chlorine. When you get into the middle of summer with longer sunny days, more UV burn off will happen.

Anticipate high FC usage like a pool party and supplement before it starts with a little liquid.

Even so, testing every 3 - 4 days is the most I like to go.
 

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Kurtomac said:
I was testing often and it was the same results so I dialed it back. I’ll go back to twice a week especially with the heat coming. What would you shoot for pre pool party FC wise?
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Before a party make sure your pH is good as this is what causes more folks to have eye irritation.

For FC, I alway just added a bottle of 8.25 bleach, which took FC up about 5. For you that would take it up about 4. Some say half way to slam level, but I think that's overkill.
 
tim5055 said:
Before a party make sure your pH is good as this is what causes more folks to have eye irritation.

For FC, I alway just added a bottle of 8.25 bleach, which took FC up about 5. For you that would take it up about 4. Some say half way to slam level, but I think that's overkill.
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my PH seems happy and stable around 7.8 and adding 4lbs of stabilizer should lower my pH to 7.5. Does low or high ph cause eye irritation?
 
Human Ph levels of tears is between 6.5-7.5 with a mean of 7.0. I try to keep my ph at 7.5 just because im an eye doctor. Anywhere between
7.5-8.0 will be a slight discomfort and not much to worry about if your water is sanitary. If you want a little more in depth, what happens is the cell wall water pump at the cornea needs to work harder to keep its dehydrated state. Usually it cant keep up so you get a swelling of the cornea and get a slight hazy vision until the proper balance is restored, few minutes usually.
 
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Kurt, one of the characteristics of an SWG is they increase the pH.. you can constantly fight it with MA additions. It seems most people let it drift up and manage it at the higher end of the range. My pH is around 7.8. I find most of the irritation is caused by CC's. Keep that in check and you will be fine. Luckily an SWG also breaks down CC's....

@Flying Tivo -I'm curious, how much does the added salinity of an SWG pool help in keeping the cornea from dehydrating... just curious to get the input of an eyeball doc. when I converted to a salt chlorinated pool years ago the kids all commented on being able to swim with their eyes open underwater easier.
 
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Added 4lbs of CYA and as expected my PH dropped .4 and my CYA went up 20. Im prob going to let my PH drift back to 7.8 before adding the other 2lbs id CYA to get to 70 to save myself an acid addition. My chlorine was a touch low at 3.6 so I bumped my run time up about 90 min and went from 20 to 25% on the controller. I’ll retest in 2 days and see how it looks. My salt is 3200 I’ll prob just leave it until I hit 3000 then add more. It’s generating just fine like it is.

here’s a link to today’s testing

 
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