A SWG is not designed to raise the FC level up from zero

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Poolsean

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TFP Expert
Apr 15, 2007
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Ft Lauderdale, Florida
Split off of this topic. JasonLion
JasonLion said:
What makes you think it isn't producing chlorine? A SWG is not designed to raise the FC level up from zero. A SWG is designed to maintain the FC level once everything is balanced and FC is in the right place to begin with.
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Jason,

It is possible to raise the FC from zero with just the salt system. It is designed to produce chlorine and not specifically to maintain a FC residual, so there's no reason that there shouldn't be a noticable increase from just using the salt system to increase the FC level.
Most manufacturers recommend adjusting your water chemistry prior to activating your salt system so that we can eliminate any possible interference from poor water chemistry, or improperly balanced water.
 
A SWG produces chlorine, just like any other chlorine. However, it produces chlorine at a relatively slow and steady rate. Meanwhile, most other sources of chlorine can add chlorine at much higher rates. When the FC level is at zero, there is almost invariably either algae or ammonia or some other similar problem going on. A SWG, with it's relatively slow and steady addition of chlorine, is often not able to produce a readable FC level in a reasonable time frame in those situations.

With ammonia in the water, the chlorine will simply vanish as it attacks the ammonia for quite sometime. With algae the chlorine will get used up fighting the algae for some time, and longer term the rate of chlorine addition may or may not be sufficient to eventually kill all of the algae. In another common condition, when CYA is zero, the chlorine will all vanish almost as quickly as it is produced as long as the sun is up, and only produce a measurable FC level at night.

The net effect is that in most pools with zero chlorine, simply turning on the SWG will not raise the FC level above zero any time soon (ammonia, zero CYA, or mild algae), and in some cases will never raise the FC level above zero (severe algae). Certainly, in some pools, say the pool was just filled with clean water, a SWG can raise FC up from zero in a reasonable time frame. But that is not the common experience as that situation is relatively rare.

When raising FC up from zero, we specifically recommend that chlorine be added quickly to shock level, something a SWG is not capable of doing. The primary design goal of a SWG is to maintain an FC level, not to add chlorine quickly. I think it is very fair to say that this is something a SWG was not designed to be able to do, even if in some situations some SWGs will be able to raise FC up from zero sooner or later.
 
Jason,

I just think it's too broad a statement to say that Salt systems are just designed to maintain a FC residual once everything is balanced. That control dial is what dictates how much chlorine you generate for your pool, along with the size of the generator cell and pump run times. While I agree that it's more of a slow and steady output, with balanced water conditions, having your control dial output too high can certainly over chlorinate a pool very quickly.
I'm making an assumption that there are many pools that run their pumps 24/7 during their pool season. With the variblespeed pumps, this is becoming more prevalant too.
Consider that a 20,000 gallon pool, circulating water at 60 gpm, will increase 2 ppm per day with 1.4 lbs of chlorine generation. 1.4 lbs/day is the output of Hayward's large cell. A Pool Pilot SC-60, 1.92 lbs/day output will increase that same pool to 2.6 ppm. Lower that flow rate to 30 gpm, with the variable speed pumps, that Hayward cell will increase the chlorine 4 ppm, while the Pool Pilot will increase to over 5 ppm, in a day.

The goal of any chlorinator is to maintain a FC level. Even with a tab feeder, a chemical feed pump, or bbb method, the goal is to maintain a FC level, if they are adjusted properly. If you over-adjust the feed rate on any system, it will over chlorinate.

I can only share with you from experience. Many pool owners start up their Pool Pilot systems in super boost mode, to get that initial chlorine dosage in their pool. Many pool owners also use the boost mode to clear up an algae bloom that appears to be starting up. There will always be some pools that require more chemicals than others to treat these conditions. I know the goal of TFP is to instruct the pool owner to hand dose chlorine, rather than using the hours of life of the cell. This is good, in the longrun, but occasional boost modes will affect cell life very minimally. As long as it's not a weekly habit, there's no harm with using the boost mode to increase chlorine levels quickly.
 
Poolsean said:
Lower that flow rate to 30 gpm, with the variable speed pumps, that Hayward cell will increase the chlorine 4 ppm, while the Pool Pilot will increase to over 5 ppm, in a day.
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Changing the flow rate changes the ppm FC delta coming out of the returns but does not change the rate of FC increase in the pool overall. It may be twice as concentrated in FC at half the flow rate but it takes twice as long for a turnover of the water -- the net result in terms of the rate of ppm FC change in the pool is the same. The cell only outputs a given amount of chlorine -- the flow rate doesn't change that output rate.

Most SWG "ratings" (which are just suggestions of a maximum size pool a given unit will support) are on the order of 1/3rd pound chlorine per day per 10,000 gallons which translates to 4 ppm FC per day with the cell running for 24 hours. However, that is only 1.3 ppm FC over 8 hours or 0.17 ppm FC per hour. Even with an oversized cell with 2x or 3x the output it is still way too low to handle getting rid of ammonia upon spring opening or getting ahead of algae growth that has already started. Realistically, the only way a "boost" mode will work effectively is if the SWG is oversized so much that the normal output setting is very low. Given how easy it is for someone to add 10 ppm FC or more to a pool immediately, it doesn't make sense for them to try and shock a pool using the SWG.
 
chem geek, I believe that when Poolsean talks about lowering the GPM, he is assuming that the pump run time will be adjusted to maintain one turnover per day. That means the SWG will be run longer and so be able to produce more chlorine.

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It seems that we mostly, or perhaps entirely, agree on the facts, but are getting stuck on wording. Several of the words we are using don't have definite fixed interpretations. We started with "not designed", which in this context is a kind of vague notion dealing with how suitable something is for a specific purpose, which is open to various interpretations both in the "suitability" and in the "purpose".

I'm going to try and be more specific. I am specifically taking about shocking the pool. Further, when we talk about shocking the pool we want a procedure that will work more than 98+% of the time, not often or sometimes, but nearly always. TFP recommends shocking when the FC level goes to zero. FC at zero does not automatically mean that shocking is required, but it is well correlated with shocking being required.

I have a significantly oversized SWG, an AutoPilot SC-60 on a 19,000 gallon pool. Running 24 hours a day at 100% it can produce about 12 ppm of chlorine. That is significantly oversized. Even though we recommend oversizing the SWG, mine is at the high end of what you tend to find in the world and dramatically larger than what is minimally required.

Even with my setup, the SWG may never produce enough chlorine to recover from a full blown green swamp. A full blown green swamp can often sustain it's self in the face of 15 or even 20 ppm of chlorine every 24 hours indefinitely. Assuming a CYA level of 60, the shocking procedure TFP recommends could easily require the addition of 80 ppm of chlorine in the first day, possibly more. Even my dramatically oversized SWG setup could not come close to that.

A typical ammonia situation has similar requirements, though the timing is not as tight. Ammonia problems can often required more than 100 ppm of chlorine, something that would take my significantly oversized SWG almost two weeks to produce running 24/7 at 100%.

Obviously these situations are not the routine day to day situation most people are in. Even a much smaller SWG run for many fewer hours can produce enough chlorine to keep up with routine demands. That is after all why people buy SWGs. Likewise, nearly all SWGs can produce extra chlorine above day to day requirements, and that extra chlorine is often enough to deal with relatively mild but still unusual events. A typical SWG set on boost/super chlorinate can handle the very beginnings of an algae bloom, or recovering from a pool party, or producing some extra chlorine for whatever reason the user wants extra chlorine.

The specific case that started this discussion was a pool with an FC level of zero. We don't know why FC was zero. Perhaps the SWG was broken. Perhaps there is a full algae bloom going on that wasn't mentioned. Perhaps they just opened the pool and there is a significant amount of ammonia in the water. Certainly there is some chance that simply going to boost/super chlorinate will take care of whatever is happening. At the same time there is a significant chance that it won't make any visible difference. To reliably recover from this situation, more chlorine needs to be added than plausible residential SWGs will be able to produce.

All of that appears to me to be straightforward and solidly based on facts. Things get much fuzzier when we explore the shadings of meaning of my original statement in full: "A SWG is not designed to raise the FC level up from zero." Certainly, there are cases where a SWG can raise the FC level up from zero. Likewise, there are cases where a SWG can not do so.

In the TFP sense of recommending procedures that are 98+% reliable, a SWG can not raise FC up from zero 98+% of the time given the distribution of situations that actually occur when FC is zero. Nor, I believe, would anyone claim that it was ever intended to. To my mind the entire discussion really comes down to that, and the disagreement is about applying that 98+% reliable rule and how fair/true/representative of the capabilities of a SWG it is to do so.
 
OK, we're in agreement. Like I said, I think the statement was a rather broad statement to make.

I would not recommend a boost cycle to clean up an algae situation, much less a green swamp. It is not designed to superchlorinate a pool. But a balanced pool, without an excessive chlorine demand, can start from 0 ppm and increase the FC level quickly, depending on cell size and pump run time.
 
it also highly depends on where your water came from

if it's a new pool and you had a truckie bring several cisterns of water around to fill it in, you never know where it came from, and how much algae it already has in it

if you filled brand new pool from tap - it's another thing

if you had an existing pool which turned into a swamp - that's again a different story.

at the end of the day, SWG is designed to produce fixed amount of chlorine at maximum output. if your chlorine demand exceeds this output due to any reason - SWG will not be able to cope on it's own.
 

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i have an intex 1x48 pool with the intex swg
i just set up the pool and i was running the swg for 7 hours a day for the first ouple of days and the FC would never come up and then i changed the cycle to 12 hours for 1 day and the FC came up to where i needed it
so the swg can generate enough to bring the FC's up bought my pool was also balanced to begin with
 
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