SWG Operation - Lessons Learned

[PatL34]

Having operated a SWCG pool since May of 1998, I thought I would give my dollarsworth of SWCG experience over the years, especially for the new SWCG owners on the forum..

Living in Central Florida allows me to run the Diamondbrite 20,000 gallon pool 8 - 12 hours a day depending on use and water temperature. The SWCG was initially an AutoPilot LS1000 with a R-15 cell. It was upgraded with a Pool Pilot DIG-220 and an SC-48 cell about 2 years ago when the R-15 cell started to die.

I had to replace the R-15 once only, and am still running quite happily on the SC-48 cell.

SWCG Operation

I had previously described in the old forum (now lost) how the cell creates the products needed to sanitize the pool and am resurrecting that procedure, with some additional explanations. There are some corrections since this was originally created, and I have to thank Chem_Geek for bringing them to light.

Salt water passing through the cell is dissociated using DC electricity applied to the membranes in the cell. This creates

Hydrogen gas, H2
Chlorine gas, Cl2

The Chlorine gas reacts with the pool water to make Hypochlorous Acid, which is the component that destroys the bacteria and chloramines in the pool.

Cl2 + H2O --> HOCL +H+ + Cl-

The Hypochlorous Acid further dissociates into Hydrogen ions and Hypochlorite ions.

HOCl <--> H+ + OCl-

As this reaction can go both ways, it depends on the pH. The higher the pH , the further it goes to the right or more dissociation. The lower the pH, the more it goes to the left, creating more Hypochlorous Acid, and making it more effective as a sanitizer.

This is why you need to keep the pH between 7.2 - 7.6 for best sanitization.

To summarize then for the non-chemists, the cell creates the components mentioned at the beginning, reacting to make Hypochlorous Acid, the main sanitizing agent. The chloramines are instantly destroyed, leaving only nitrogen and hydrogen coming from the returns, and retaining chlorine for use in the pool because of the high CYA content.

Lessons Learned

pH - Maintain between 7.2-7.6 using muriatic acid. Most of the other manufacturers also recommend this pH range. If you decide to use dry acid, then you will have to add salt to maintain the salt level. The effect of dry acid is to raise the TDS level as well as lower the pH and is not part of the process. I prefer to keep it simple with Muriatic Acid.

Salt Level - Different manufacturers call for different salt levels for their products. The Poolpilot calls for 2500 - 3500 ppm, Watermaid for 6000 ppm, and Aquarite from 2700 - 3400 ppm. For the Poolpilot, maintaining 3000 - 3500 ppm seems to work fine for me.

BTW, when adding salt in granular form to a plaster pool that has a concrete coping, be very careful not to spill any salt granules on the concrete. It will eventually create a hard deposit that will have to be removed with hammer and chisel. Wash any areas with pool water using a bucket back into the pool or use a garden hose.

Flow through the Cell - Several factors can reduce the flow through the cell, such as high differential pressure through the filter, which may need to be cleaned or backwashed. The use of solar or other forms of heating too can have an effect, as can vacuuming. With the Autopilot or Poolpilot, there is a springloaded check valve that helps to maintain flow through the cell at low flows. Other factors are scale buildup on the trisensor affecting both flow and salt concentration. This requires cleaning the unit with dilute Muriatic acid, even though the cell might not have scale. Whenever I clean the cell the trisensor is included. I use a Muriatic acid concentration of 1 part acid to 4 parts water. Always add the acid to the water, never the other way round.

Calcium Hardness - Keeping the CH at no more than 300 ppm for a plaster pool helps to keep the cell clear of scale. Check the cell once a month for any scale buildup, and clean according to the manufacturer's instructions, or the method mentioned above. A vinyl pool has to have no more than 120 ppm, but this may be different for other types of non-plaster pools.

Refill Water - Use of softened city water as refill helps to minimize the buildup of calcium hardness as well. Use of well water especially in Central Florida should be avoided, as if it contains Hydrogen Sulfide gas, it can destroy the active coating on the cell fairly rapidly. If it has to be used, either find a way to bypass the cell, or shut the circulation down while refilling to allow the gas to escape. A further help would be to use a filter that can remove iron, as this a major problem here in Central Florida.

Stabilizer (CYA) - Most of the manufacturers recommend 60 - 80 ppm, but I have been able to run with nearly 0 ppm in winter to about 50 ppm in the summer, with a maximum of 60 ppm. These figures have worked for me, but some units may require more. The reason the manufacturers require a high CYA concentration is because the cell produces a high concentration of chlorine at the cell membranes, and most of it is used in instantly destroying the chloramines. By keeping the CYA level high, it maintains the chlorine needed in the body of the pool.

Testing - Having a very good testkit is paramount for checking SWCG operation. Besides the regular chemicals to be tested, a drop type testkit for salt is highly recommended as a backup for pH meters. These units have to be calibrated frequently for reliable operation, no matter who tells you different. Ben's PS234 testkit is the choice of record for this in my opinion. Test strips should ONLY be used if there is nothing else, and are not recommended for SWC or regular bleach operation in my opinion.

Startup and Upsets - If the pool system has to be shut down for the winter, then on Spring startup, it is my recommendation and the manufacturer's not to turn on the SWCG until the system has been stabilized using bleach, and only bleach, as well as the other chemicals including salt to the manufacturer's specifications.

Similarly for upsets, there is no need to increase the SWCG loading, as this reduces cell life unnecessarily. Add bleach as needed to bring the sanitization level back to normal for your system. The SWCG is designed to maintain a steady chlorine level only, provided the water chemistry is monitored frequently.

For a new plaster pool, some plaster vendors recommended not adding salt for a SWCG for at least a month, until the plaster has had time to cure. Most of the time the salt can be added straightaway.

Also make sure that all leaves and debris are removed from the pool, skimmers and pool pump basket on a regular basis, otherwise the cell is working longer to remove this debris.

Cable Connections - need to be checked both to the cell and control sensors for good electrical contact on a regular basis, as this seems to be the weakest area when a control unit is not functioning properly. Scaling of the sensors can be another problem and have to be checked if there is scale buildup on the cell.

Pros

The unit saves having to lug Liquid Chlorine or Bleach and pucks, which have to be kept in a cool environment tightly sealed.

The great advantage is that it is a constant source of Chlorine, assuming the rest of the pool chemistry is maintained properly.

Cost wise I have found it is equivalent to running a 220 watt bulb for whatever hours of the day the unit is running. Based on the PoolPilot I have, it is about $22 per month for an 8 - 12 hour day, and that includes the cost of the cell over a 5 year life.

As the price of oil goes up, so will the cost of electricity and the cost of manufacturing bleach. SWCGs will start to pay for themselves in the long run. The initial cost will offset any price increases in bleach later on.

Cons

According to most AG pool manufacturers, they are not recommending these units for their pools and you will have to check the warranty. Similarly, SWCG manufacturers are not recommending them for AG pools and will give fair warning if you do. Check with both types of manufacturer bofore investing in an AG pool/SWCG combination.

The initial cost can be the problem here, but once set up and running, the return in ease of maintenance will be well worthwhile. Prices from pool equipment suppliers on the Internet give you a lot more choices for shopping around for the best and lowest prices.

I have found no real problems other than cable and sensor connections. Electricity has a way of finding the weakness in any electrical circuit.

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Any input from the "seasoned" SWCG owners would be appreciated, including manufacturer's reps.

I did this mainly as a general explanation for the new SWCG owners, to help them operate their particular setup.

Hope this all helps.

Pat

[gwrace1]

I started up a new 26000 gallon pool in March of this year with an Aquarite SWG. I have been able to maintain chlorine levels by running our 2 speed pump on low for about 12 hours per day at night. The SWG is set at 40% with a salt level of 3500 PPM. The only adjustments I've needed to make are for PH. It takes a dose of Muriatic Acid about once per week. I am currently running approximately 35-40 PPM stabilizer and maintaining a FC of 4PPM. The water has been crystal clear since startup and I have never shocked the pool.

My only water source was iron rich well water. To deal with the metals I placed an iron removing 2 micron whole house filter ahead of the softener and used softened water to fill the pool. It took 5 days and many regeneration cycles to complete the process. While the pool was filling I added a metal out product and Polyquat 60%. Once the pump and filter were working I allowed this mixture to circulate for several days with the SWG off. I'm using Zeobest filter media in a 26" Pentair sand filter on a two speed pump. No bleach or chlorine was added to the pool.

Day 4 I switched on the Aquarite and gave it a few days to bring up the chlorine levels. Once that was done I added stabilizer via the skimmer to the 35-40 PPM level. The pool has been simple to maintain ever since.

A quality test kit with salt level is a must.

[tonyl]

Thanks Pat,
That's a great post. I remember vaguely the lost version so I printed this new one. Chemistry isn't my forte but your explanation is one that I get.

Question: When the first cell "started to die", what was the indication? The reason I'm asking is my cell output seems to go up every year with the other variables the same. I assumed (incorrectly?) that it would suddenly die.

Thanks, Tony

[PatL34]

Thanks Pat,
That's a great post. I remember vaguely the lost version so I printed this new one. Chemistry isn't my forte but your explanation is one that I get.

Question: When the first cell "started to die", what was the indication? The reason I'm asking is my cell output seems to go up every year with the other variables the same. I assumed (incorrectly?) that it would suddenly die.

Thanks, Tony

You will find that the DC volts go up and the DC amps go down, indicating a higher resistance between the membranes as the coating wears out. The chlorine output starts to go down as well.

In your case, you appear to have a cell that seems to "rejuvenate" itself. I would expect that might happen if you acid wash the cell at the end of the season, but I suspect something else might be happening. It should lose efficiency as it gets to the end of its life.

Hope this helps.

Pat

Pat

[tonyl]

Well, when I typed my output goes up I should have said output SETTING......ahhh....what a difference a word makes.

Thanks for the info Pat, I'll have to keep an eye on it.

Tony

[clone1008]

Pat,

Very informative write-up, especially since I'm considering the conversion myself. In your "Lessons Learned", can you tell me have there been any negatives? What about corrosion over an extended period of time? Any long term damage to the tile grout or coping? I'm just a little leary after getting caught up in the "Baquicil Movement" about 7 years ago and the horrors involved with that.

[PatL34]

Pat,

Very informative write-up, especially since I'm considering the conversion myself. In your "Lessons Learned", can you tell me have there been any negatives? What about corrosion over an extended period of time? Any long term damage to the tile grout or coping? I'm just a little leery after getting caught up in the "Baquicil Movement" about 7 years ago and the horrors involved with that.

The only real negative I found was having to replace the powerboard on the control unit 3 times because of bad quality control on the original LS1000 unit.

Corrosion at the salt levels that the Pool Pilot I use (3000 - 3500) has not given any instances of corrosion, other than having to wash the aluminum pool rakes and attachments, which were never designed for a saltwater pool any way. If you do find corrosion to the tile grout or coping, that is evidence of bad workmanship on the part of the pool builder.

In addition, I had to add a fresh water shower to prevent my wife and her swimsuit from being corroded away. BTW she was a pediatric nurse and understands that salty water hurts the eyes less than fresh water.

I think you will find that SWCG operation is a far cry from Baquacil and you should find it less troublesome. Having said that make sure you keep your pool chemistry up to par, and you should have no problems.

Hope this helps in your decision.

Pat

[clone1008]

The only real negative I found was having to replace the powerboard on the control unit 3 times because of bad quality control on the original LS1000 unit.

Corrosion at the salt levels that the Poolpilot I use (3000 - 3500) has not given any instances of corrosion, other than having to wash the aluminum pool rakes and attachments, which were never designed for a saltwater pool any way. If you do find corrosion to the tile grout or coping, that is evidence of bad workmanship on the part of the pool builder.

In addition, I had to add a fresh water shower to prevent my wife and her swimsuit from being corroded away. BTW she was a pediatric nurse and understands that salty water hurts the eyes less than fresh water.

I think you will find that SWG operation is a far cry from Baquacil and you should find it less troblesome. Having said that make sure you keep your pool chemistry up to par, and you should have no problems.

Hope this helps in your decision.

Pat

Pat,

Thanks for the help. You raise another interesting topic...will the salt water at that low of a level really mess up swim suits? Also, do you really feel the need to fresh water rinse in this type of water? I know the salty feeling of swimming in the Gulf but I didn't think this would be an issue in a pool. In fact most of the websites talk about the "good" feeing skin and no more bleached out suits.

Ric

[PatL34]

Pat,

Thanks for the help. You raise another interesting topic...will the salt water at that low of a level really mess up swim suits? Also, do you really feel the need to fresh water rinse in this type of water? I know the salty feeling of swimming in the Gulf but I didn't think this would be an issue in a pool. In fact most of the websites talk about the "good" feeing skin and no more bleached out suits.

Ric

I think you were taking me too seriously. The fresh water shower is more a convenience to remove the salt from the body and suit, before going in and taking a regular shower. Even public pools without salt have showers for this purpose. And yes you do have "good' feeling skin in a salt water pool, probably better than in the sea.

But even when swimming in the Gulf, the salt content is 3 - 4 times higher than in a salt water pool, but you still take a fresh water shower to remove the sea salt. Sea water to my knowledge has never ruined a swimsuit.

Hope this clears things up.

Pat

[clone1008]

I think you were taking me too seriously. The fresh water shower is more a convenience to remove the salt from the body and suit, before going in and taking a regular shower. Even public pools without salt have showers for this purpose. And yes you do have "good' feeling skin in a salt water pool, probably better than in the sea.

But even when swimming in the Gulf, the salt content is 3 - 4 times higher than in a salt water pool, but you still take a fresh water shower to remove the sea salt. Sea water to my knowledge has never ruined a swimsuit.

Hope this clears things up.

Pat

Point well taken...and thanks for the hygene tips...LOL...just kidding...thanks for all the info you've been very helpful!

Ric