A beginners guide to SWG's

[Desiato]

I've been looking after my pool the TFP way for many years now thanks to the great advice I received here. It's a little harder to do in Spain as drop test kits are not readily available but I managed to find one and the pool has been looking great ever since. I dabbled with the idea of going SWG but the initial cost put me off as my only real expense was a daily bottle of bleach for €1.10 at the height of summer (one a week in the winter) and it would take several years for an SWG to be cost effective.

Now that bleach is €1.60 a bottle I'm thinking about SWG's again but it's becoming clear I don't know much about them. Over the years I've met several people who have raved about their "chlorine free pools" because they've got a SWG and one recently told me his pool water doesn't sting the eyes as a chlorine pool would. I held my ground on the stinging eyes comment saying that a correctly balanced chlorine pool doesn't sting the eyes either (mine doesn't) so he must have come across badly balanced pools but he then went on to say that it works by electrolysis, so the salt gets converted to very volatile chlorine so there is no chlorine in the pool. My gut reaction was to say, Really? No chlorine, Are you sure? but as we all know, a little knowledge is a dangerous thing so I just shrugged and said "ok". Another thing he said was that if the water is 30'C you need to run the SWG for 15 hours, 28'C for 14 hours etc so the number of hours is half the temperature level in centigrade. Is that true?

There's a lot there and I felt very silly not knowing what to say so feel it's time for me to find a 'SWG for Dummies' website and fully expected to find one here, can anyone point me in the direction of where to start?

Another friend has had a SWG for many years at his previous house and has just installed one at his new house but was completely unaware of Cyanuric Acid. He said he just controls the PH with acid and that's all he has to do, apart from change the cell once every5/6 years. I checked online later and saw that SWG pools should have between 60-80ppm of CYA so what has been his cost for not having any? A shortened life span of the cell? More salt required? Longer running times of the SWG? Would like to be able to give accurate advice as to why he should add some CYA to his pool.

So in summary, no chlorine with a SWG? Volatile chlorine? No need for CYA?, Really?

Thanks for any help in growing my knowledge and maybe going SWG myself if the pennies can stretch to it.

 

[Mdragger88]

A pool with a swg is a chlorine pool. The swg is just feeding the pool for you instead of manually dosing.
Yes - swg’s use electrolysis to convert the salt into chlorine and when it gets used up it then turns back into salt free to begin the process again to put it simply. It’s definitely still chlorine.
More info here

SWG How It Works - Further Reading

www.troublefreepool.com

A mis- managed swg pool can cause stinging eyes, itchy skin etc. No different than any other pool as elevated cc’s &/or improper ph are generally the cause of those things not the chlorine itself.

You should run a swg long enough to produce the amount of fc your pool consumes daily. The run time & percentage depends on your pool volume, cell output (based on cell size), & fc demand. That looks different for different pools in different seasons.
Its not a specific number based on temperature (although obviously the fc demand in the peak of summer is generally higher leading to longer run times/%).

Without adequate cya the fc the cell produces can get consumed by the sun as quickly as it’s made as a swg produces fc slowly over a long period of time.
All swg cells have a finite lifespan (usually around 7-10k hours @100%) so the more you have to run it the faster you reach that 7-10k hours.
It is recommended that you get a cell that is rated for at least 2x’s your pool’s volume so that you have plenty of wiggle room & don’t have to run it @ 100% around the clock to meet your fc demands resulting in a longer cell life in people years.

Hope this helps you have a better understanding

 

[mgtfp]

Another thing he said was that if the water is 30'C you need to run the SWG for 15 hours, 28'C for 14 hours etc so the number of hours is half the temperature level in centigrade. Is that true?

As Mdragger88 already said, there is no exact number like that. You could argue that the water temperature is an indicator for how much sun exposure the pool gets (as long as there is no heater involved, and probably with some delay) and temperature itself will also accelerate chlorine oxidisation processes, so there certainly is a tendency that you have to increase the chlorine production with rising water temperature. But the amount of FC in ppm added to the pool each day depends not only on the run time, but also on all the other parameters that Mdragger88 has mentioned.

It might be a good reminder though that, when you notice the water temperature creeping up in spring or plummeting down in autumn , it might be wise to check that your FC is where you want it, and keep adjusting the SWG production (via run-time and/or output-percentage).

 

[Desiato]

Without adequate cya the fc the cell produces can get consumed by the sun as quickly as it’s made as a swg produces fc slowly over a long period of time.

Right, so no CYA = SWG running for longer, using more electricity, using up the life of the cell and using more salt. There's some pretty good reason to add some CYA.
I've just watched a video by some guys that call themselves Orenda Technologies and one of them said that 50ppm of CYA or even down to 30pmm is what they recommended and that the 60-80 ppm was an outdated number and newer thinking has brought this number down. He even went as far as saying 70ppm was so high it would start to have a detrimental effect on maintaining a balance, any thoughts on that?

Thanks for your reply and the link, very helpful

 

[ajw22]

I've just watched a video by some guys that call themselves Orenda Technologies and one of them said that 50ppm of CYA or even down to 30pmm is what they recommended and that the 60-80 ppm was an outdated number and newer thinking has brought this number down. He even went as far as saying 70ppm was so high it would start to have a detrimental effect on maintaining a balance, any thoughts on that?

Orenda has things they want to sell you, we don't.

We have seen no scientific evidence to support what they claim.

I suggest you ask them to show scientific evidence for their claims.

 

[Mdragger88]

using more salt.

The swg doesn’t use up the salt
The only way to lose salt is through water replacement with fresh water.

Orenda has things they want to sell you,

Yup

 

[mgtfp]

Right, so no CYA = SWG running for longer, using more electricity, using up the life of the cell and using more salt. There's some pretty good reason to add some CYA.

Another reason is that without CYA, you are also missing its moderating effects. Without CYA, running FC somewhere between 0.1 and 0.2 would give you the HOCl equivalent to the target-FC in a pool with CYA following the TFP recommended FC/CYA Levels. Which gives you absolutely no maintenance buffer, just one kid peeing into the pool will bring that to zero.

Without CYA, FC 0.64 ppm is equivalent to SLAM level.

 

[Desiato]

The swg doesn’t use up the salt

Just so I'm clear, my friend doesn't have any CYA in his pool so the chlorine is being used/burned off quicker. The SWG converts salt into chlorine so if he needs more chlorine doesn't that mean he will need more salt? Sorry, as you can see, I know bugger all about SWG's and the more I read, the more complicated they sound.

 

[mgtfp]

The SWG converts salt into chlorine so if he needs more

SWG turns salt (the chloride part of it) into chlorine. UV light and use of chlorine for sanitation/oxidation turns chlorine back into chloride. The chlorine doesn't leave the water, it just changes oxidation level. The SWG is basically a recycler.

 

[Desiato]

Another reason is that without CYA, you are also missing its moderating effects. Without CYA, running FC somewhere between 0.1 and 0.2 would give you the HOCl equivalent to the target-FC in a pool with CYA following the TFP recommended FC/CYA Levels. Which gives you absolutely no maintenance buffer, just one kid peeing into the pool will bring that to zero.

Without CYA, FC 0.64 ppm is equivalent to SLAM level.

Taking this post as a whole, I'm picking up that a salt water pool without any CYA is a bad idea and if that's what he is doing, he doesn't really know what he is doing. Unfortunately my knowledge of SWG's barely registers a pulse so I couldn't fully understand all of the technical references but I get the gist, thanks.

 

[jedigrover]

Taking this post as a whole, I'm picking up that a salt water pool without any CYA is a bad idea and if that's what he is doing, he doesn't really know what he is doing. Unfortunately my knowledge of SWG's barely registers a pulse so I couldn't fully understand all of the technical references but I get the gist, thanks.

Pretty much. CYA does other things than just act as a sunscreen for the chlorine. It also makes the chlorine less irritating to the skin. Essentially, it just keeps the extra (not being actively consumed) chlorine in storage (like a capacitor, in electronics) and when the FC level falls, it gives up some to act as sanitizer. At least, that's the way I like to think of it.

Depending on where you live / how much sun exposure you get, your CYA need could vary a bit. I live in Texas, and with the sun exposure here, I have to keep CYA at 60 minimum to have any success. Anything less and my SWG won't be able to keep up even running at 100%. Those in more northerly climes may find they need less.

 

[Desiato]

Anything less and my SWG won't be able to keep up even running at 100%. Those in more northerly climes may find they need less

The TFP guidelines say 60-80 for CYA in a SWG pool so doesn't that suggest that Texas would be closer to 80 and the north 60? If dipping below 60 is a problem for you wouldn't it be better to maintain a level of 70 to 80?

 

[Mdragger88]

The TFP guidelines say 60-80 for CYA in a SWG pool so doesn't that suggest that Texas would be closer to 80 and the north 60? If dipping below 60 is a problem for you wouldn't it be better to maintain a level of 70 to 80?

Just like with a manually chlorinated pool it varies by the time of the season - around 60 in the shoulder times & around 80 at the peak of the summer. Vs 30-50 w/ a manually chlorinated pool.

 

[Desiato]

Just like with a manually chlorinated pool it varies by the time of the season - around 60 in the shoulder times & around 80 at the peak of the summer. Vs 30-50 w/ a manually chlorinated pool.

Yeah I get that but if I said that I kept my CYA at 30 in my non SWG pool and all kinds of chaos ensued it if drops to 29, wouldn't it make sense to keep it at 40? Passed my bedtime here so adios for now.

 

[Mdragger88]

Yeah I get that but if I said that I kept my CYA at 30 in my non SWG pool and all kinds of chaos ensued it if drops to 29, wouldn't it make sense to keep it at 40? Passed my bedtime here so adios for now.

Yes - they’re just suggested ranges - each person can do what works best for them based on their conditions/circumstances.

 

[proavia]

Yeah I get that but if I said that I kept my CYA at 30 in my non SWG pool and all kinds of chaos ensued it if drops to 29, wouldn't it make sense to keep it at 40? Passed my bedtime here so adios for now.

Well - it's virtually impossible to measure a CYA of 29 - anywhere between 21 and 29 is rounded up to 30 anyway.
The scale of the tube is logarithmic and not linear - half way between 20 and 30 is NOT 25 on the scale.

If CYA tests at 20 instead of 30 next month, add 10 ppm using PoolMath
If something doesn't "seem right" during the month - test and adjust accordingly.

 

[jedigrover]

The TFP guidelines say 60-80 for CYA in a SWG pool so doesn't that suggest that Texas would be closer to 80 and the north 60? If dipping below 60 is a problem for you wouldn't it be better to maintain a level of 70 to 80?

It really varies for each individual situation. I also run borates in my pool, which tends to act as an algaestat. And I do maintenance doses of polyquat algaecide (60% poly algaecide)--which is also much more of an algaestat than algaecide, despite the marketing [this is a deviation from the standard TFP method, but I have old plaster and a history of black spot algae in the pool, so it's "insurance" to me]. I run at a high enough chlorine residual (6ppm, typically...10% of the CYA value) which gives me a little headroom for particularly UV-intensive days. Also consider that the higher your CYA, the less effective your chlorine. That's why I run my chlorine at 10% the CYA value. So if I went to 80 on CYA, I'd keep a chlorine residual of 8. Obviously, that means more use of the cell, so there is an economical balance to work there too. I shoot for keeping just enough CYA to protect the chlorine & high enough chlorine to keep algae at bay--especially the tough stuff like cyanobacteria ("black spot algae"). If I get a little dusting of algae after a storm (that's generally when it will get me), I will either goose my salt generator for a day or two, or stop by the hardware store for a gallon of 10% bleach and knock it out before it becomes a problem.

I've found that in the dog days of summer (July-August) I might have to go to 70 CYA. But I don't ever go beyond that, as I learned when I was a novice (before TFP) to stay away from the danger zone (anything close to 100). Trichlor pucks really got me bad in the past, and I don't want to repeat that ever again.

 

[Desiato]

Well - it's virtually impossible to measure a CYA of 29 - anywhere between 21 and 29 is rounded up to 30 anyway.
The scale of the tube is logarithmic and not linear - half way between 20 and 30 is NOT 25 on the scale.

If CYA tests at 20 instead of 30 next month, add 10 ppm using PoolMath
If something doesn't "seem right" during the month - test and adjust accordingly.

I was simply replying to this statement

I have to keep CYA at 60 minimum to have any success. Anything less and my SWG won't be able to keep up even running at 100%.

My simple logic was, if the guidelines are 60-80 and you keep yours at 60 and you get problems if it drops below 60, raise it to 70! Yeah, I should have realised it was TOO simplistic. jedigrover explained his CYA levels in more detail in the last post so sorry for any confusion, I wasn't talking about my CYA levels although I never knew about this logarithmic scale so that's good to know.

Off to read about SWG's