- Jan 4, 2016
- 5,288
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- Chlorine
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For some reason, my answer won't post, so I sent it via PM, and will try to post it here again in a little while.
Build-up on Salt Cell
- Thread starter Mandy
- Start date
- Jan 4, 2016
- 5,288
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- 44000
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- Chlorine
- Salt Water Generator
The layered exchange is done by sucking water from the bottom of the pool, while gently adding the lighter fresh water at the top, so the main body of water stays fairly still.
So yep, you would put the vacuum plate in the skimmer and attach a manual vacuum hose to the hole in the skimmer plate, and close off any bypass in the skimmer plate. If you have a manual vacuum, you can attach that to your pole, and then put the vacuum head at the deepest point, turned upside down, so now that's your pump intake.
Then you set up your fill hose to add water at the top. A great method is to put your fill hose in the skimmer and let the water flow out through the skimmer throat, into the pool. You might need to wedge down the skimmer weir flap with a bit of timber or something. Another method is to set a bucket on your top step, put the fresh water hose in it, and let the water overflow the bucket and into the pool. Open the fill hose wide open to save time; weigh it down with something if need be.
First up, get your fill hose flowing. If your bucket has litres marked on it, time it a couple times to see how long it takes to fill and then you'll have your replacement flow rate, and you can calculate how long it will take to fill, say, 3/4 of your pool. That's how long you'll need to keep the fill line running, in total.
Now start your pool pump, with filter set on waste. Keep pumping until it gets down a bit below the skimmer. It can suck a bit of air, but if it's sucking too much and you hear the pump losing prime and labouring, stop at that point. For example, maybe you can get down 150 mm (6") below the skimmer. Make a note of the time, and then see how long it takes to get back up to near overflowing. That will tell you how long you can leave it filling and unattended.
When it's full again, drain off some more, and keep repeating until your fill hose has run long enough. The key is to keep the body of water still while you're doing this, i.e. no brushing, no dogs, no swimming, cover on if you have one, etc.
This is best done continuous, but an overnight break with still water won't ruin it entirely. It won't be quite as good, because there is some diffusion between the salty water and the fresh water, but it's fairly slow.
So yep, you would put the vacuum plate in the skimmer and attach a manual vacuum hose to the hole in the skimmer plate, and close off any bypass in the skimmer plate. If you have a manual vacuum, you can attach that to your pole, and then put the vacuum head at the deepest point, turned upside down, so now that's your pump intake.
Then you set up your fill hose to add water at the top. A great method is to put your fill hose in the skimmer and let the water flow out through the skimmer throat, into the pool. You might need to wedge down the skimmer weir flap with a bit of timber or something. Another method is to set a bucket on your top step, put the fresh water hose in it, and let the water overflow the bucket and into the pool. Open the fill hose wide open to save time; weigh it down with something if need be.
First up, get your fill hose flowing. If your bucket has litres marked on it, time it a couple times to see how long it takes to fill and then you'll have your replacement flow rate, and you can calculate how long it will take to fill, say, 3/4 of your pool. That's how long you'll need to keep the fill line running, in total.
Now start your pool pump, with filter set on waste. Keep pumping until it gets down a bit below the skimmer. It can suck a bit of air, but if it's sucking too much and you hear the pump losing prime and labouring, stop at that point. For example, maybe you can get down 150 mm (6") below the skimmer. Make a note of the time, and then see how long it takes to get back up to near overflowing. That will tell you how long you can leave it filling and unattended.
When it's full again, drain off some more, and keep repeating until your fill hose has run long enough. The key is to keep the body of water still while you're doing this, i.e. no brushing, no dogs, no swimming, cover on if you have one, etc.
This is best done continuous, but an overnight break with still water won't ruin it entirely. It won't be quite as good, because there is some diffusion between the salty water and the fresh water, but it's fairly slow.
Needsajet: Thank you for the great explanation. I may not get to it for a week or so but will let you know how it goes. Given the water needs to be as still as possible it's probably best I don't bother with the phosphate treatment. I'll check its level before and after water exchange
- Jan 4, 2016
- 5,288
- Pool Size
- 44000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
No worries and good luck with it. It's a good time of year to do it rather than have to muck around during swim season! 
For clarity I need to ask ........... Do you think the scale issue with my SWG came about due to the combined level of sulfates [EDIT] and phosphates [END EDIT] reaching a certain point? In other words, if I only had [EDIT] either sulfates or phosphates but not both, then no matter what the level, [END EDIT] would this problem have occurred?
My CH level on 01/06/18 was 290ppm. Today it is reading 180. My tap water has CH of 110. If I plug these numbers into PoolMath it tells me I would have to have replaced 61% of my water to achieve this result. During this time I have replaced water 11 times due to general topping up, backwashing, rinsing and vacuuming to waste.
Todays phosphate level is also down 547ppb since it was last tested. So thinking along the lines of the issue coming about due to the combined level reaching a certain point I decided to go ahead with the phosphate treatment, thereby lowering one part of the equation. But if this assumption is incorrect then no harm done.
And given these drop in numbers could it be possible I've already replaced enough water to reduce my potential for scale in my SWG? Or, are the sulfates that were introduced from using dry acid and MPS just nasty and they should be removed no matter what the level?
My CH level on 01/06/18 was 290ppm. Today it is reading 180. My tap water has CH of 110. If I plug these numbers into PoolMath it tells me I would have to have replaced 61% of my water to achieve this result. During this time I have replaced water 11 times due to general topping up, backwashing, rinsing and vacuuming to waste.
Todays phosphate level is also down 547ppb since it was last tested. So thinking along the lines of the issue coming about due to the combined level reaching a certain point I decided to go ahead with the phosphate treatment, thereby lowering one part of the equation. But if this assumption is incorrect then no harm done.
And given these drop in numbers could it be possible I've already replaced enough water to reduce my potential for scale in my SWG? Or, are the sulfates that were introduced from using dry acid and MPS just nasty and they should be removed no matter what the level?
Last edited:
- Jan 4, 2016
- 5,288
- Pool Size
- 44000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
Bit of a slow answer here! I was up the Gold Coast golfing
There's a pretty good chance you've exchanged enough water and all is well.
I don't have the specific chemistry expertise, but I've researched it here and elsewhere a fair bit. There are unknowns because little is known about the unique conditions inside an SWG cell because it's difficult to test. For normal pool pH and temperature, sulphate levels have to be very high for calcium sulphate scale to occur.
If it were mine, I'd leave it and not replace any more water. There's every chance the sulphates are low enough that they won't cause any more trouble. I'd clean the cell and then just keep an eye on it for a while. Or just leave it as-is, and see if the scale on the cell dissolves or stays the same. It sounds like you have a great handle on TFPC and keeping the water balanced so I'm betting you won't see it again.
There's a pretty good chance you've exchanged enough water and all is well.
I don't have the specific chemistry expertise, but I've researched it here and elsewhere a fair bit. There are unknowns because little is known about the unique conditions inside an SWG cell because it's difficult to test. For normal pool pH and temperature, sulphate levels have to be very high for calcium sulphate scale to occur.
If it were mine, I'd leave it and not replace any more water. There's every chance the sulphates are low enough that they won't cause any more trouble. I'd clean the cell and then just keep an eye on it for a while. Or just leave it as-is, and see if the scale on the cell dissolves or stays the same. It sounds like you have a great handle on TFPC and keeping the water balanced so I'm betting you won't see it again.
It would appear my phosphate level was way higher than anticipated. It took 4 treatments to reduce its level to 53 ppb. This could indicate a level of around 14000 ppb to begin with! So lots of water has been exchanged thereby reducing my sulfate level as well. I'll keep an eye on my salt cell but don't anticipate any future problems with it. Test results at end of treatment:
FC 7
CC 0
pH 7.6
TA 70
CH 200
CYA 40
Salt 2200
Water temp 9.5C
CSI -0.68
Adding CYA, calcuim and salt in coming days. Thank you all for your advice and assistance, very much appreciated
FC 7
CC 0
pH 7.6
TA 70
CH 200
CYA 40
Salt 2200
Water temp 9.5C
CSI -0.68
Adding CYA, calcuim and salt in coming days. Thank you all for your advice and assistance, very much appreciated
- May 23, 2015
- 24,411
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Very interesting. Here’s how to identify scale -
Use full strength muriatic acid and put some scale scrapping into it.
Calcium carbonate - will dissolve rapidly with lots of fizzing and bubbling.
Calcium sulfate - scale will slowly dissolve with no bubbles at all
Calcium phosphate - scale will not dissolve at all
Usually one needs both high phosphate levels AND high calcium hardness to get scaling but the inside of the SWG cell can be quite a different environment than the bulk pool water.
Use full strength muriatic acid and put some scale scrapping into it.
Calcium carbonate - will dissolve rapidly with lots of fizzing and bubbling.
Calcium sulfate - scale will slowly dissolve with no bubbles at all
Calcium phosphate - scale will not dissolve at all
Usually one needs both high phosphate levels AND high calcium hardness to get scaling but the inside of the SWG cell can be quite a different environment than the bulk pool water.
- Jan 4, 2016
- 5,288
- Pool Size
- 44000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
Sweet!!! Great to see a tough one solved, and thanks again for being a forum supporter
Matt, do you think it would be worthwhile adding this information regarding identifying types of scale to the Calcium Scaling page in Table of Contents? Apart from helping to identify the type of scale causing a problem it would also assist in rectifying the problem...............which in my case was to remove phosphates and exchange water to reduce sulfates.