- Nov 23, 2014
- 213
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
I’ve loved my SWG over the past few years. Even with having to add salt and clean the cell every few months, it’s so much easier than dealing with buying, transporting, storing and deploying liquid chlorine constantly. But a recent salt-stain event had me questioning the SWG if there is iron staining from the salt. So I tested several brands and types of salt.
If you want to skip the detail, I concluded: Buy the salt with least amount of iron and, when distributing it, dissolve/distribute it well, not leaving a layer on the pool surface for more than a few minutes. Diamond Crystal and Clorox had the most iron, “Morton” and “Salinity” brands had less iron. “Aquasalt” had the least iron (zero), but tough to find at a reasonable price.
Along the way I got “pool-stored” a bit, that and other details follow….
My “stain event” occurred when I dumped a full 40 lb bag of Clorox pool salt on the top step (as I usually do), but about an inch deep of salt sat there covering the large oval step for a couple hours (after I was interrupted by a post-hurricane power outage). When I came back and brushed it into dissolution there was a noticeable brown stain left on the step – picture enclosed. This prompted me to test several different salt brands for iron content.
Results of the iron tests follow, but I might first note that I usually maintain my chemistry well and keep CSI very close to zero, but this day/week the PH may have floated up towards 8.0 or 8.2 as I was dealing with other post hurricane matters. I think I read that high PH may increase sensitivity to iron staining. Full chemistry at the time: FC 5, PH 8.2, TA 50, CA 200, CYA 25, Salt 2700, Phos 150, WaterTemp 87, CSI 0.1
My test method was arguably extreme, but it was just for comparative purposes. I dissolved 1 lb of each salt brand into 32 oz of water, then tested with a “Hanna Iron (Fe²⁺ & Fe³⁺) Chemical Test Kit model HI3834. Instructions state that it detects the combination of ferrous and ferric ions by first reducing the ferric ions to ferrous. Given the extreme ratio of salt to water, not all salt dissolved, in each case a layer of salt remained on the bottom of the container. And yes, my test reagents expired 7 years ago, but the results are similar to what I was seeing when testing years ago on well water that stained concrete over the course of a year or more from well water irrigation.
Except where noted most of these brands can be had for about $7-$9 per 40lb bag at various big box discount stores. As noted Salinity and AquaSalt were pricier. Detailed results follow, in order of most iron to least iron, noting this may vary from batch to batch. When you research how it’s mined and packaged, there is a lot of variation, depending on many factors such as the original source and all the equipment that comes in contact with the salt along the way.
Edit 1/4/2024: See also post #71 far below, where @AUSpool kindly re-summarized these results to include some additional insights we had gathered about purity and ingredients - from the web and from statements on the salt bags.
Diamond Crystal Water Softener pellets: ~1.0 PPM (mg/L). Slow dissolve, about 45 minutes if they’re not stacked. The pellets look like peanuts.
Diamond Crystal Splash Ready Pool Salt: ~0.5 to 0.75 PPM. Dissolves a lot like morton into smaller clear glassy crystals, then rather slow to finish dissolving over perhaps an hour.
Clorox: ~0.5 PPM (mg/L) iron, maybe higher. Fast & easy to dissolve but clumps if stored for awhile. This is what stained my step surface when an inch of it was left on the surface for a couple hours. Noting again that my PH was running high at 8.0 or 8.2 at the time of stain.
Morton Professional’s Choice Pool Salt: 0.2 ppm / just a trace of iron. A bit slow to dissolve as it first half-dissolves into clear smaller crystals, much like the diamond crystal splash ready.
Salinity brand...... Just a trace of iron, $15/ bag from pool store. Label states “high purity salt for swgs - premium salt blend fine granular quick dissolving with *stain inhibitor” (says imported, ‘Amanaplast’ logo) - Note this finer powder, like Clorox, dissolves quickly when swished or brushed but when spread 1/4" deep takes longer than some others. This would be runner up to the winner, except for the fact that we have no idea what the ”stain inhibitor” chemical is, no ingredients listed. A bit of sequestrant perhaps? Most TFP folks don’t like adding unknown chemicals.
Aquasalt: ZERO trace of iron. This would be the clear winner – except for the price. Very fine and almost powdery, dissolves easily, much like Clorox. But it’s $25/bag from Leslies, delivered. Leslies asks only $12.50 per bag but charges another $12.50/bag for delivery and they won’t ship to the store. I called corporate and a store, no joy. A friend of mine has access to a local wholesale distributor and they told him the price would be $7.50/bag but they never have it and seem uncooperative to order it. Weird that.
More thoughts/speculation:…. Reading the instructions on many salt bags, they advise of course to distribute the salt around the pool, don’t do what I did and leave it stacked in one place for hours. But that seemed bogus to me, since I wondered if I’m simply staining the entire surfaces – just more slowly, gradually. So I continued to wonder about the long term effect of having added more than 1000 lbs of salt over a few years. Still, the pool water itself registers zero trace of iron using the Hanna test kit and all the surfaces look pristine, except for my “stain event” – that I cleared with a sockfull of ascorbic acid powder.
Then I speculated that, like CYA and salt, the summer rains and resultant overflow are probably clearing the iron just like that same overflow & splashout removes CYA and salt itself. Unless the iron is stuck stained to surfaces, gradually staining all surfaces, ugh.
So – not to worry? After all that hoopla and work, I suppose I’ll just buy Morton pool salt and dissolve & distribute it well – LOL.
“Poolstored” sidebar…. While buying the “Salinity” brand from the local PinchAPlenty store I asked the tech if they ever carry Aquasalt. He said no, and he added that he would never buy salt from the big box discount stores. Naturally I asked if he used the stuff I was buying from his store. He said no. So I asked where he buys his, and he said “I can’t tell you – since I work here”. Sigh. If anyone finds a good way to acquire Aquasalt I’m all ears!
As implied by the picture, for stain removal I first started with some vitamin C tablets, then acquired a 2 lb container of ascorbic acid for $17 from wallymart, then used the sock – very simple and easy. Then I got to wondering what happens to the iron that I “wipe off” with ascorbic acid – does it settle elsewhere eventually? Some good threads exist here in TFP on iron removal – many thanks to @Texas Splash, @JoyfulNoise, @Brian Malone, @BoDarville and many others for all those comments in threads such as getting rid of iron and rust and Polyfill and iron binding during AA treatment and related threads. Just for grins I fashioned some polyfill around my cartridge filter and also tried the “aquabag” for a few days on a return port – but never captured any visible iron using those methods. Then again those attempts may be moot since I did not run the PH and FC back up to get any iron to precipitate. And reading through those iron removal threads I never figured out if sequestrant should be present when trying to precipitate the iron. Alas – the surfaces look great and the water is totally clear, so I may have just been wasting even more time!
Thoughts and opinions always welcome and appreciated. Happy SWG-ing and salting everyone. … Joe
If you want to skip the detail, I concluded: Buy the salt with least amount of iron and, when distributing it, dissolve/distribute it well, not leaving a layer on the pool surface for more than a few minutes. Diamond Crystal and Clorox had the most iron, “Morton” and “Salinity” brands had less iron. “Aquasalt” had the least iron (zero), but tough to find at a reasonable price.
Along the way I got “pool-stored” a bit, that and other details follow….
My “stain event” occurred when I dumped a full 40 lb bag of Clorox pool salt on the top step (as I usually do), but about an inch deep of salt sat there covering the large oval step for a couple hours (after I was interrupted by a post-hurricane power outage). When I came back and brushed it into dissolution there was a noticeable brown stain left on the step – picture enclosed. This prompted me to test several different salt brands for iron content.
Results of the iron tests follow, but I might first note that I usually maintain my chemistry well and keep CSI very close to zero, but this day/week the PH may have floated up towards 8.0 or 8.2 as I was dealing with other post hurricane matters. I think I read that high PH may increase sensitivity to iron staining. Full chemistry at the time: FC 5, PH 8.2, TA 50, CA 200, CYA 25, Salt 2700, Phos 150, WaterTemp 87, CSI 0.1
My test method was arguably extreme, but it was just for comparative purposes. I dissolved 1 lb of each salt brand into 32 oz of water, then tested with a “Hanna Iron (Fe²⁺ & Fe³⁺) Chemical Test Kit model HI3834. Instructions state that it detects the combination of ferrous and ferric ions by first reducing the ferric ions to ferrous. Given the extreme ratio of salt to water, not all salt dissolved, in each case a layer of salt remained on the bottom of the container. And yes, my test reagents expired 7 years ago, but the results are similar to what I was seeing when testing years ago on well water that stained concrete over the course of a year or more from well water irrigation.
Except where noted most of these brands can be had for about $7-$9 per 40lb bag at various big box discount stores. As noted Salinity and AquaSalt were pricier. Detailed results follow, in order of most iron to least iron, noting this may vary from batch to batch. When you research how it’s mined and packaged, there is a lot of variation, depending on many factors such as the original source and all the equipment that comes in contact with the salt along the way.
Edit 1/4/2024: See also post #71 far below, where @AUSpool kindly re-summarized these results to include some additional insights we had gathered about purity and ingredients - from the web and from statements on the salt bags.
Diamond Crystal Water Softener pellets: ~1.0 PPM (mg/L). Slow dissolve, about 45 minutes if they’re not stacked. The pellets look like peanuts.
Diamond Crystal Splash Ready Pool Salt: ~0.5 to 0.75 PPM. Dissolves a lot like morton into smaller clear glassy crystals, then rather slow to finish dissolving over perhaps an hour.
Clorox: ~0.5 PPM (mg/L) iron, maybe higher. Fast & easy to dissolve but clumps if stored for awhile. This is what stained my step surface when an inch of it was left on the surface for a couple hours. Noting again that my PH was running high at 8.0 or 8.2 at the time of stain.
Morton Professional’s Choice Pool Salt: 0.2 ppm / just a trace of iron. A bit slow to dissolve as it first half-dissolves into clear smaller crystals, much like the diamond crystal splash ready.
Salinity brand...... Just a trace of iron, $15/ bag from pool store. Label states “high purity salt for swgs - premium salt blend fine granular quick dissolving with *stain inhibitor” (says imported, ‘Amanaplast’ logo) - Note this finer powder, like Clorox, dissolves quickly when swished or brushed but when spread 1/4" deep takes longer than some others. This would be runner up to the winner, except for the fact that we have no idea what the ”stain inhibitor” chemical is, no ingredients listed. A bit of sequestrant perhaps? Most TFP folks don’t like adding unknown chemicals.
Aquasalt: ZERO trace of iron. This would be the clear winner – except for the price. Very fine and almost powdery, dissolves easily, much like Clorox. But it’s $25/bag from Leslies, delivered. Leslies asks only $12.50 per bag but charges another $12.50/bag for delivery and they won’t ship to the store. I called corporate and a store, no joy. A friend of mine has access to a local wholesale distributor and they told him the price would be $7.50/bag but they never have it and seem uncooperative to order it. Weird that.
More thoughts/speculation:…. Reading the instructions on many salt bags, they advise of course to distribute the salt around the pool, don’t do what I did and leave it stacked in one place for hours. But that seemed bogus to me, since I wondered if I’m simply staining the entire surfaces – just more slowly, gradually. So I continued to wonder about the long term effect of having added more than 1000 lbs of salt over a few years. Still, the pool water itself registers zero trace of iron using the Hanna test kit and all the surfaces look pristine, except for my “stain event” – that I cleared with a sockfull of ascorbic acid powder.
Then I speculated that, like CYA and salt, the summer rains and resultant overflow are probably clearing the iron just like that same overflow & splashout removes CYA and salt itself. Unless the iron is stuck stained to surfaces, gradually staining all surfaces, ugh.
So – not to worry? After all that hoopla and work, I suppose I’ll just buy Morton pool salt and dissolve & distribute it well – LOL.
“Poolstored” sidebar…. While buying the “Salinity” brand from the local PinchAPlenty store I asked the tech if they ever carry Aquasalt. He said no, and he added that he would never buy salt from the big box discount stores. Naturally I asked if he used the stuff I was buying from his store. He said no. So I asked where he buys his, and he said “I can’t tell you – since I work here”. Sigh. If anyone finds a good way to acquire Aquasalt I’m all ears!
As implied by the picture, for stain removal I first started with some vitamin C tablets, then acquired a 2 lb container of ascorbic acid for $17 from wallymart, then used the sock – very simple and easy. Then I got to wondering what happens to the iron that I “wipe off” with ascorbic acid – does it settle elsewhere eventually? Some good threads exist here in TFP on iron removal – many thanks to @Texas Splash, @JoyfulNoise, @Brian Malone, @BoDarville and many others for all those comments in threads such as getting rid of iron and rust and Polyfill and iron binding during AA treatment and related threads. Just for grins I fashioned some polyfill around my cartridge filter and also tried the “aquabag” for a few days on a return port – but never captured any visible iron using those methods. Then again those attempts may be moot since I did not run the PH and FC back up to get any iron to precipitate. And reading through those iron removal threads I never figured out if sequestrant should be present when trying to precipitate the iron. Alas – the surfaces look great and the water is totally clear, so I may have just been wasting even more time!
Thoughts and opinions always welcome and appreciated. Happy SWG-ing and salting everyone. … Joe
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