cell life in SWG

iam4iam

LifeTime Supporter
May 5, 2012
231
Johnson City, TN
I've read numerous posts about which SWG to choose (when I decide I can afford one). I would want something very basic, but my main concern in terms of budget would be how long to expect the cell to last. I read in pool school that cells typically last 3-5 years. Am I totally oversimplifying it, or does SWG cell life basically depend on the "demand" of chlorine asked for vs. how much it can produce? For example, will the cell on an SWG that can produce 2 lbs/day of Cl last about 4 times longer than one on a unit that can produce only 0.5 lbs/day, or is cell life more dependent on other factors? If this logic is correct, it would be most cost-effective to buy a unit rated for a much larger pool and just run it at a lower % output. Am I at least basically correct or am I out in left field?

The comparison chart at www.saltwaterpool.com seems to be a good starting point.
 

jblizzle

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May 19, 2010
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Tucson, AZ
We recommend getting a cell that is 1.5-3 times larger than your pool for the very reason you described.

Being able to run on a lower setting should allow the cell to last longer offsetting the extra cost of the larger cell.

Posted with Tapatalk ... sorry if I sound short ... hate typing on phone :)
 

iam4iam

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May 5, 2012
231
Johnson City, TN
I'm assuming the "rating" is based on the rate of chlorine production, so isn't the CPR (chlorine production rate) the most important piece of information? See example below:
Aquarite (40K): CPR = 1.4 lbs/day
CPSC36: CPR = 1.69 lbs/day

Assuming these CPRs are accurate, doesn't that imply that the CPSC36 has a "larger" cell?

That brings up another question: Is bigger always better? (Are all the cells essentially the same other than size?)
 

JasonLion

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First, you can go too large. You don't really want a cell more than 3 (or maybe 3.5) times the size of your pool. If the cell is really large you have to turn the percentage down so low that you have little control over the FC level.

Second, there are many many differences between brands. The underlying technology is all essentially the same, but cost, reliability, convenience, build quality, customer service, and so on all vary from one company to another.
 

jblizzle

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I think you are correct. It is the possible production (based on running 24 hours) that matters.

Since your pool will need the same amount of FC regardless of the system, It does look like the CPSC36 would have to run less than the Aquarite (40K) ... ASSUMING that they both define the production rate the same.

There are some people that have cells that seem too big. The Pentair (I think it is this one) only allows adjusting the % in 20% increments if you do NOT have the automation system. So, they have to set to 20% and then shorten the run time to reduce the chlorine production. Now, with automation, they could dial the % down more and then could use longer pump run times if required.

Honestly, I am not exactly sure what the difference in the different cell sizes is. I don't know if it is the number of plates, or it if is the amount of power that can be used in the cell.
 

JasonLion

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jblizzle said:
Honestly, I am not exactly sure what the difference in the different cell sizes is. I don't know if it is the number of plates, or it if is the amount of power that can be used in the cell.
Different manufacturers do things in different ways. Usually, larger cells have some combination of larger plates and/or more plates. Some other factors also affect the cell "size", but generally a single manufacturer tends to stick with a single design and vary the total plate area.
 

jblizzle

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JasonLion said:
jblizzle said:
Honestly, I am not exactly sure what the difference in the different cell sizes is. I don't know if it is the number of plates, or it if is the amount of power that can be used in the cell.
Different manufacturers do things in different ways. Usually, larger cells have some combination of larger plates and/or more plates. Some other factors also affect the cell "size", but generally a single manufacturer tends to stick with a single design and vary the total plate area.
Thanks.
 

iam4iam

LifeTime Supporter
May 5, 2012
231
Johnson City, TN
I generally run my pump for about 10 hr/day. Any less and the water seems to lose its "brilliance." Therefore, I could calculate DCR (daily chlorine requirement in lb/day) to maintain FC = 3 and either get a unit with a CPR of 2 times my DCR and set it on 50% (or just under if possible) or one with CPR 4 times my DCR and put it on 25%, with the cell probably lasting longer in the latter case?

If this is how it works, how would I calculate my DCR? Are the "lbs" of chlorine referred to in advertised CPR units pounds of Cl or pounds of HOCl? I typically use 80-96oz of bleach per day currently, but that's to maintain FC = 5-8 @ CYA = 70.
 

iam4iam

LifeTime Supporter
May 5, 2012
231
Johnson City, TN
I ended up biting the proverbial bullet and investing in a SWG this year. I went with a Circupool RJ45. My FC level has been around 7 for almost a month now, which I know is higher than necessary, and not my goal, but I have been gradually decreasing pump run time and checking after a week or so. I went from 6 hrs/day to 5 hrs/day to 4 hrs/day (all at 100%). It is curious how I've decreased pump run time by 33% and FC still hovers at the same level. I suppose it is a combination of CYA level and the fact that the more FC that is present, the faster UV from the sun depletes it. I thought about going down to 3 hrs/day run time, but the pool has never been this clear and I don't want to risk losing clarity to save $5/month, so today I turned the cell down to 80%. My plan is to keep decreasing output % until FC hovers around 5. (CYA is >40, but that is all I can say with certainty. This is another frustration, but I will post this in another topic and link to it here when I do).
JasonLion said:
If the cell is really large you have to turn the percentage down so low that you have little control over the FC level.
I'm wondering how low I'm going to have to go. I know I maxed out on the cell size (13,800 gal. pool), but how low is too low? In the end I suppose there is no harm in having FC at 7, but I obviously want to prolong the the cell life if I can. (See, I am still on topic!)
 

jblizzle

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By running at the higher FC levels, you are using up more the the cells life than required.

There is no too low as far as the output setting.

Part of your problem is that your CYA appears to be too low. We recommend 70-80ppm for SWG pools. If you raise the CYA, you should be able to turn the cell % output down a good bit.

No reason to post your question in another thread instead of here.
 

iam4iam

LifeTime Supporter
May 5, 2012
231
Johnson City, TN
jblizzle said:
There is no too low as far as the output setting.
JasonLion said:
If the cell is really large you have to turn the percentage down so low that you have little control over the FC level.
Not trying to start an argument, but these two statements seem to be contradictory. If Jason (Lion) could explain how control over the FC level might be reduced, that would be great.

As for CYA, I've been trying to raise it to 70 for over a month. I've added 7 lbs of stabilizer already this season: 2 lbs on 5/28, 2 lbs on 6/21, and 3 lbs on 7/1. Each time, I've waited about a week to measure, and I'm not seeing significant changes. I've purchased the 50 ppm solution from Taylor to make sure I'm testing correctly, so that is not the issue. When it arrived, I concluded that what I had been "guessing" as 60 ppm was really more like 40. That was when I made the most recent addition (3 lbs), which should raised the level to almost 70 ppm, but the actual reading only went up to about 50 ppm. I was baffled at it only being at 40 ppm after adding 4 lbs (71 oz actually) to whatever the pool started with this season, which shouldn't be very different from last season, since I didn't even close the pool this winter, and I know I had some CYA last year. (I measured it at 70 last year, but that was probably not the best measurement. Still, I'm sure it wasn't super low.) I'm starting to wonder if the stabilizer at Walmart (Aqua Chem) is junk. Hard to believe something labeled "100% Cyanuric Acid" would be anything but that, but that's the only explanation I can come up with. I've also considered liquid stabilizer, but it's just too expensive.
 

jblizzle

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We are saying 2 different things.

You can run the SWG at as low a setting as you want.

JL was saying you can have a problem if the SWG is way too big. At low output settings, a small % change becomes a large FC difference. For example, if you put a 40k cell on a tiny pool, it can be hard to dial in because a change from say 5% to 10% would double the FC. The problem with the Pentair SWG is you only get settings every 20% if you do not have an automation system.
 

linen

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Jul 30, 2010
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Twin Cities, MN
How are you adding the stabilizer?
Do you have an autofill on your pool and/or have you noticed need for a lot of makeup water?
 

JasonLion

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To elaborate a little on what jblizzle said: A small SWG might typically run at 50% (setting), if you needed a little more chlorine, say 3% more chlorine, you have a step size of 2%, i.e. increasing output to 51% (setting) increases the total amount of chlorine produced by 2%, so you need to go to a 4% increase (ie 52% on the SWG), which wastes a little cell life (we actually wanted 51.5%, but that isn't an option), but not much. Now do that again, but this time assume you have a really big SWG and typically run at 10% (setting). If you need 3% more chlorine, you have to go to 11% (setting), which is a 10% increase, way more than the 3% increase you wanted and thus wasting more cell life than you would with a smaller unit. (I know, a little confusing, since I am using percentage two different ways, but hopefully you can follow along.)
 

iam4iam

LifeTime Supporter
May 5, 2012
231
Johnson City, TN
Thanks to both Jasons. You both made sense. Once I ready the explanation of JL's original statement, I felt like a block head for not getting what he was saying to begin with. :hammer:

linen said:
How are you adding the stabilizer?
1st 2-lb addition: sock hanging in front of one of the returns. Sock "busted" and most ended up at bottom of pool, but I stirred it all up with my pool brush.

2nd 2-lb addition: sock in skimmer basket for a while, but then heldsock in front of return and "helped" the CYA dissipate from the sock by squeezing it. (No patience.)

3-lb addition: sock hanging in front of one of the returns
linen said:
Do you have an autofill on your pool and/or have you noticed need for a lot of makeup water?
No and not hardly. Due to this year's heavy precipitation. I've actually pumped a few inches out to waste! I don't think I've added water once! Even so, the "new" water, whether from rain or my house's water source, wouldn't alter the CYA concentration more than a few percent. (Just did some mental arithmetic. One inch at the surface equals about 2% of the 13,800 gallons, so it would take 5 in. of new water to alter the CYA concentration by 10%, which would barely be noticeable on the CYA test.)

That last statement reminds me of another, more frivolous, question. Would a 10% decrease in CYA concentration be the same change in depth in the CYA reading tube for all levels? (CYA concentration as a function of depth of test water in the reading tube appears to be exponential.)