SWCG/Non SWCG suggested CYA and FC levels

[Fuldo]

A member recently suggested that my best option to minimize pool maintenance was to convert to SWCG. I'm now seriously thinking of doing that because the relative who monitors and maintains my pool during the summer is taking an extended vacation this summer.

I've been researching all aspects of the conversion. The one thing that bothers me is the very high CYA (70-80) and rather low minimum FC (3) and target FC (5) suggested here. It just seems like there's little margin for error and considerable margin would likely be required if the pool isn't checked frequently. My pool survived a bad experience with very high CYA and chlorine tablets. I've finally got the water chemistry as perfect as possible and I haven't had to shock since resolving the basic problems about 9 months ago. I'm rather reluctant to tempt fate again.

It appears that a SWCG pool has proven more stable and bullet-proof than a Non-SWCG pool. It also appears that it can survive with the high CYA and low FC. Is the high CYA strictly to minimize chlorine use/generation so the system can be sized smaller and use less energy? Using liquid chlorine in my case seems to work great at CYA 30 or so and keeping FC in the 2-7 range results in a maximum chlorine usage of about 30 ounces of 11% per day in the summer. It's much less than that other times of the year. I think that equates to the equivalent of only 1/4 pound of chlorine per day, much less than the capacity of the smallest common SWCG generators. I was actually thinking of going with a 1.5#/day generator for greater capacity, life and efficiency. I think my use is low, especially for Florida, because the entire pool is screened and only gets direct sun for probably 7 hours per day.

In my case is CYA 50 and FC target 5 unreasonable? Won't this still result in low chlorine generation, excess capacity and long life while giving me considerable sanitation margin?

 

[mknauss]

You can run at the lower CYA with a SWCG. Our suggestion of a higher level for CYA is that it minimizes the loss of chlorine to UV, which you have less than normal due to the screen.

The other reason a lower FC can be carried with a SWCG is that it is always adding chlorine, each day. When you manually dose with liquid, you have large peak and valleys of FC in your pool. With a SWCG, not so much.

So try it out at 50 CYA and 5 FC. You may have to run your SWCG more than if you carried a higher CYA, but that is an economic discussion, not a chemistry one!

Take care.

 

[JoyfulNoise]

I operate my pool with a CYA at 90ppm and an FC usually no higher than 3ppm even with direct intense AZ sun on the pool for up to 10 hours per day. I’ve never had a problem.

I would say the lowest you should go in CYA is 60ppm for an SWG pool as our levels recommend. These levels are used by thousands of pool owners every year and they always produce clean and clear pools with happy pool owners. Your pool will be just as great.

 

[JohnT]

The FC values in the chart are based on both the experience of pool operators of levels where algae isn't an issue and calculations of effective chlorine levels, so the numbers in the chart will work. The higher CYA levels are specified by the manufacturers to provide a longer cell life.

Remember that high CYA (within reason) is generally only a problem if you have to SLAM the pool. Since SWCGs are less prone to algae for reasons not entirely understood, it's not as big of a concern.

You should also be aware that although an SWCG automates chlorination, it does introduce a need for more frequent pH adjustment since the chlorine production process tends to move pH fairly quickly.

 

[Fuldo]

Wow, thanks for the responses and information. That AZ system speaks for itself and amazes me. I guess it's a whole new world when salt is added.

My biggest concern is that the pool could go many days without anyone checking it and if the SWCG system failed the pool would quickly turn ugly. Mid summer this pool will drop about 2 PPM FC each day at CYA 40 and FC about 5. I guess the chances of a system failure are rather low and keeping the FC marginally higher wouldn't buy much time regardless. I guess it's now a question of when to do it not if. Maybe I'm best off waiting until mid summer to make the switch so I can monitor it and characterize it while I'm there on my "two week summer vacation".

What normally happens when the cell needs cleaning? Do most systems give some advanced warning and if so how long in advance? Is it worth cleaning periodically before it needs it to help avoid it shutting-down unexpected while unattended for some time?

 

[mknauss]

IF you are able to maintain your CSI at or below 0.0 you will never have to clean the cell. Most SWCG's use reverse polarity to shed any minor build up of calcium. Most also have a warning light on them that tells you to clean them (though some are time based, not need based).

pH management even during your absence will be necessary. We leave for extended periods of time and we have a pool service that visits weekly, cleans the pool and adds acid, as necessary. Not ideal, but functional.

 

[Jimrahbe]

Fuldo,

Keep in mind that nothing prevents you from maintaining a higher FC than is in the charts... It is just not needed. I personally like to use the 'target" value as my unofficial minimum. So if the target is 5, I try to run 6 or 7. It means I use more chlorine than I need to, but it gives me that latitude to test a little less often..

So, if you plan to go on vacation for 2 weeks, just increase the Output percentage on the SWCG, or up the pump run time on your pump,and you should be good to go..

I believe my SWCG manual says to check for scale about every three months.. I looked at it about the 6 month mark and it was clean.. I then went another year and checked again. At that point (year and a half) it had just a little scale, which I cleaned... Keep in mind that was my pool and each pool and water is a little different. As long as you keep your chemicals per the TFP standards, I don't see an issue...

I do try and keep my CSI level a little negative... but I don't obsess over it..

Thanks,

Jim R.

 

[BasicTek]

I run my 1.45 lb SWG for an 11K screened pool in FL for a summer max of about 20% for 4 hours and I try to keep my CYA at 80 but it drops a little faster than expected and I've been using pucks to maintain it (had a bunch leftover). My FC demand rarely exceeds 1.5 a day if I keep my CYA over 70, I've noticed my FC demand jump to about 2.5 when I let the CYA drop to 60 or below. I try to keep the FC around 5-6 but this SWG constantly overproduces and I have to shut it down for a day when it does and dial down the %. I've only had the FC go low (due to laziness) while the pool was covered from December to January and the average pool temp in the 70's I was running the SWG @ 5% for 2 hours and I didn't test for a month+. The CYA dropped to 40 and FC to 1.5. I added a couple pucks, found some leftover liquid stabilizer, turned up the SWG to 50% for a couple days, and was over chlorinating again with CYA of 70 by the end of the week. Laziness is not following the TFP method but the SWG has made me overconfident since it almost always overproduces. Coming up on my 1st year I've never had to clean my cell. CSI is probably average around -.2

 

[Fuldo]

Thanks guys, very helpful.

I'll need to watch my PH more closely, it presently tends to drift upwards dragging my CSI positive by up to 0.20. My CSI is negative to 0 at ideal PH range.

Nice to know that a visual observation can give an idea of when the cell may need cleaning.

BasicTek's post is very informative because his pool and enclosure is very similar to mine, our pools are only about 25 miles from each other and his system is also similar to what I was considering. That system seems to be so oversize that it's hard to throttle-back, I wonder if I should consider something smaller. I'm under the impression that chlorine loss rate increases with FC level so at some point it will come to equilibrium is left with too high a dosing rate, isn't that so? I don't understand why CYA would drop drastically over just a month without water changes, it isn't lost with SWCG use is it?

 

[mknauss]

CYA is not lost due to SWCG use. It is oxidized over time by typically 3-5 ppm per month. There are anecdotal observations of being greater than that and less than that.

UV is typically what oxidizes the CYA. As your pool is in a screen, I would suspect your UV impact is minimized.

 

[BasicTek]

My CYA didn't drop from 80 to 40 over a month more like 70-40 in 3 months, I hadn't tested CYA since November. Still I think losing 10 a month in the winter was more than I expected (that's why I wasn't testing for it) like Marty said 3-5 is what's expected. I also lost 10 - 15 a month over the summer, but we had an exceptionally wet summer last year culminating with Irma. When I started here I had 220 CYA so I totally understand why you don't want to raise it, but it's really not a big deal to maintain 70-80 with SWG especially in FL.