Fine Tuning a Salt Water Pool

[BigTallGuy]

I installed a SWCG about a month ago, and have gained an incredible amount of knowledge and information on this Forum. I realize that These are FAQ's but here goes. Approx 11,500 gallon AG pool.

First my readings from this afternoon:

FC 5.0
TC 5.0
CYA 50
Salt 3300
TA 120
pH 7.4

I am currently running the system 5.0 hours per day at 100% output. The FC reading above was taken at 4:00 p.m. approximately 15 hours after the pump shut off, and 4 hours before it is scheduled to kick back on. I have read the "Best Guess" thread regarding the CYA to FC ratio and would like to know if these levels apply to salt Water pools as well as Traditional Chlorine pools.

I am having to add Muriatic acid to keep the pH level down and have read a lot of info on his forum regarding this. I seem to be adding less amounts less frequently as my CYA level rises. I did nurse the CYA up slowly, and I have cut my "on" time from 8 hours to 6 hours to 5 hours.

It would seem likely to me that I can reduce my amount of "on" time or reduce the output percentage still further. With respect to the rising pH level, which would be better, the shorter actual "on" time or the lower percentage?

I would appreciate any and all comments or feed back.

[aylad]

I'm sure the SWG experts (I'm not one!! ) will be by to confirm this soon, but with respect to the rising pH, my understanding is that it is not the percentage of chlorine generated that raises the pH, but rather the operation of the unit itself. So to slow the pH rise, I'd say cut back on the run time. (I'll be interested in the expert's respnses too, because I'm currently taking care of a friend's pool with a SWG and have the same issue)

Janet

[polyvue]

FC 5.0
TC 5.0
CYA 50
Salt 3300
TA 120
pH 7.4

I am currently running the system 5.0 hours per day at 100% output. The FC reading above was taken at 4:00 p.m. approximately 15 hours after the pump shut off, and 4 hours before it is scheduled to kick back on. I have read the "Best Guess" thread regarding the CYA to FC ratio and would like to know if these levels apply to salt Water pools as well as Traditional Chlorine pools.

I am having to add Muriatic acid to keep the pH level down and have read a lot of info on his forum regarding this. I seem to be adding less amounts less frequently as my CYA level rises. I did nurse the CYA up slowly, and I have cut my "on" time from 8 hours to 6 hours to 5 hours.

It would seem likely to me that I can reduce my amount of "on" time or reduce the output percentage still further. With respect to the rising pH level, which would be better, the shorter actual "on" time or the lower percentage?

The chemical equilibriums represented in the CYA/FC ratio charts apply to both salt and non-salt pools.
[EDIT 6/4/10] No. See Watermom's comment and my mea culpa, below [END-EDIT 6/4/10]

If you find the FC climbing too high for your liking you can reduce pump time and/or turn down the percentage on the cell.

You'll get accustomed to this tuning and learn over time what works for your pool. Since rising pH can be an indirect result of cell chlorine production (per accepted wisdom) and a direct outcome of carbon dioxide outgassing from splashing and other types of aeration, this too may be a matter of trying different protocols until one works. pH volatility can be reduced somewhat by allowing your Total Alkalinity to come down over time and (if I understand this correctly) by the addition of borates. When modulating pH rise in my own pool, I reduce TA and cut back the time water features are running (including spa spillover).

BTW I'm not the SWG expert Janet referred to -- just an SWG learner.

[Watermom]

The chemical equilibriums represented in the CYA/FC ratio charts apply to both salt and non-salt pools.

This is something we are currently investigating so that we can provide accurate information for our members who have a SWC. Clarifications will be posted shortly.

[BigTallGuy]

I am very curious to hear any new "Best Guess" data. Please keep me in the loop. I have learned that FC readings of 5.0 are reasonably good for a Salt water pool, so I am reasonably comfortable with these numbers.

This question has been rolling around in the back of my mind for sometime now. Is there any information on the Chlorine curve in a normal day? Here is what I mean and I can already guess that a lot will depend upon the CYA, the amount of sunlight, and other factors.

If I check the FC at daybreak with my old cheap plastic tester (no pool stores are open at daybreak and I can't test in the dark) I would get a reading of 5.0 as an example. Then if I re-test FC again at sundown, I would think I should see a significant loss say down to 3.0 or something. Now these are not actual readings they're just examples.

When I test in the late afternoon when I get home from work, my actual Chlorine readings are 5.0ish, so would this tend to indicate that I am starting out at something like 10.0 in the morning, or is the normal curve much flatter than that?

BTW, my old cheap plastic tester only goes to 3.0 on the FC scale and says 1.0 - 1.5 FC is "Ideal". I know I need a new tester, and trying to get meaningful readings that are actually "off the chart" with my old one is difficult at best. Again my thought is, I am comparing apples to oranges with a Salt vs. Traditional Chlorine systems.

As always all comments are welcome and appreciated. BTDG

[rpoldervaart]

I don't think it really matters whether you lower your "on" time or lower the percentage. I'm assuming by "on" time, you are referring to the time the filter pump is actually "on."

The pH rise is attributed to the amount of time the SWCG is actually generating chlorine. The generation is binary, or it is either generating, or it is not generating. The percentage is the percentage of time that the cell is actually generating chlorine. If you have the percentage at 100%, then the cell is generating 100% of the pump time. If you have it at 50%, the cell cycles on and off and is only generating only 50% of the time, and the other 50% of time it is just passing water through the cell. During the non-generation time, it is not contributing to the pH rise.

For example, say you run your pump for 8 hours, and the percentage is set to 50%. You're generating chlorine for approximately 4 hours. You can lower the generation time to 3 hours by either reducing your pump time to 6 hours, or reducing the percentage to 35-40 percent. Either way, you reduced the generation time by an hour, and both ways should impact the pH rise the same amount.

HOWEVER, in practice, I think you want to run the filter pump (regardless of whether or not you have a salt pool) long enough to filter your pool volume at least once per day. Once you have that run time established, then you adjust the percentage on the chlorine generator to keep your chlorine level where it should be. There may be other reasons to adjust the pump time, but in general, I don't think you should change the pump time to adjust the chlorine level. You should change the percentage to adjust the chlorine level.

This is all based on my own pool and reading this and other forums to learn. Hopefully someone will correct me if I have given any false information.

[BigTallGuy]

Yes, "ON" time is when the Pump, Filter and SWCG are all running (it is a package deal). I have it set up as you say in a binary system either everything is on or everything is off.

My thought is this, I'd like to run the system as few hours as necessary to reduce the electric bill. I traditionally ran the pump for 4-5 hours a day before I installed the SWCG.

I will see if I can find any stats on the Pump as far as gallons per minute or per hour when I get home to calculate a complete water turnover.

Thank you very much for your reply. BTDG

[polyvue]

This sentence does not appear to be correct information. This is something we are currently investigating so that we can provide accurate information for our members who have a SWC. Clarifications will be posted shortly.

I should cut back on my nightly dose of cyanuric acid... drinking it hasn't helped my neurons one bit. In my pool (SWG chlorination), I try to maintain a rough minimum FC level of 5% CYA. My understanding, despite what I said above, is that non-SWG pools do better to target 7-8% minimum Free Chlorine. With CYA of 50 ppm, that's 2.5 ppm FC for SWG pools, 4.0 ppm FC for non-SWG pools.

Thanks for catching this!

[BigTallGuy]

I should cut back on my nightly dose of cyanuric acid... drinking it hasn't helped my neurons one bit. In my pool (SWG chlorination), I try to maintain a rough minimum FC level of 5% CYA. My understanding, despite what I said above, is that non-SWG pools do better to target 7-8% minimum Free Chlorine. With CYA of 50 ppm, that's 2.5 ppm FC for SWG pools, 4.0 ppm FC for non-SWG pools.

Thanks for catching this!

Polyvue, LOL amen on the nightly dose of CYA it is worse than diet soda. Your post struck a cord with me and I can't thank you enough. On Memorial Day, we had all the kids in the "New" pool. CYA was 50, FC was 5.0+, pH was 7.6, Salt was 3300. Everyone agreed there was slight eye irritation. I have cut my FC down to be more in line with your numbers. I will keep you posted.

[polyvue]

Polyvue, LOL amen on the nightly dose of CYA it is worse than diet soda. Your post struck a cord with me and I can't thank you enough. On Memorial Day, we had all the kids in the "New" pool. CYA was 50, FC was 5.0+, pH was 7.6, Salt was 3300. Everyone agreed there was slight eye irritation. I have cut my FC down to be more in line with your numbers. I will keep you posted.

Interesting.... When you state that FC was 5.0+ this implies that you're utilizing an OTO (yellow) test that only measures to 5 ppm chlorine. I've had occasion to swim in water with greater than 5 ppm Free Chlorine but did not experience any eye irritation. Are the combined chloramines (CCs) testing at .5 ppm or less? The 3300 ppm salt should further alleviate eye irritation because a salt level up to ~7000 ppm is closer to the typical salinity in tears.


Note for the humor-impaired: Do Not Drink cyanuric acid. I was joking.... as was BTDG. Stick to diet soda.