Swg Chemical/corroding Problems

[rocket]

Put pool in this Summer. Pool guys filled it up and added to much salt (3900). So I had to drain down and add more water (3200 now). However after getting refilled water levels were way off. CA was 8. Calciaum hardness way low and FC way high. So they added proper chemicals, but I have since noticed skimmers screws and now automatic pool cover screws corroding like crazy. Not sure if happened before or after chemicals added. And it was the 2nd or 3rd time they tested the water and added chemicals. They run it thru a computer and it tells them what to add so I don't know why they can't get it right. Also I have a automatic SWG. The ORP is set to 650, but it never seems to be operating at 650. Before the last batch of chemicals were added it would read 615-620. Since the last batch was added now it says 690-710. It is supposed to make the right amount of chlorine to maintain 650, but as mentioned it has been all over the place. Also when I try to test the levels with strips. The strips are crazy off. I have two different types. One would say the FC was 15-20. The other would say 2-4. All the other levels tested were way off on the different strips from each other as well. Needless to say I am upset. I was wary of a SWG and corrosion after reading the blogspot pool guy, but my contractor said he has never had any problems. I am especially wary of it because unlike a few screws or a ladder, the pool cover cost about $10,000 and I am afraid the motor/rails/box etc will get eaten up. So far only a couple screws on it is corroding. But I am worried about the aluminum rails and the "coated steel box". Also concerned about the expensive stamped concrete surrounding the pool. Not sure what to do as obviously nothing is working right. Living in Midwest the season is drawing to a close.

[chem geek]

Answered here.

[jkusmier]

You might read a pool corrosion study that Chem Geek posted in this forum sometime ago. It specifically found that excessive chlorine levels (20ppm +) are the most common/likely cause of corrosion issues in swimming pools. (You mentioned that your FC was as high as 20ppm per test strips* - see my * at the end).

The article also found that the corrosive effects of salt levels up to 3000ppm were insignificant, and noted that experience w/ a SWG in Australia (where SWG's first appeared over 30 years ago and are presently used in some 90% of pools) suggested the threshold corrosion point for salt water levels to be 6000ppm. Note that all forms of chlorine sources for pool eventually breakdown, and one of the principal residual products is... SALT! Pool owners living in warm climates (like north Texas as featured in the TV news story) who don't need to partially drain their pools for winterization probably have fairly high salt levels in their water after a few seasons. The salt levels required by SWG's are roughly equivalent to those found in human tears.

Just as importantly, low CH (calcium hardness) levels like yours (8 is extremely low) make the water very aggressive/corrosive. Also, you didn't mention your pH levels.

I have personally experienced a few minor corrosion issues in my pool, which was installed in 2007 and is equipped w/ a SWG. The issues were heavy corrosion of the brass pilot screw holding my SAm light in place (builder should have known to never use brass, I replaced w/ a stainless steel screw) and some rust around the tread bolts and caps on my pool ladder (the ladder is powder-coated. In retrospect, I should have specified a stainless steel ladder, but I didn't know anything about pools when we built in 2007 and wanted white. S.R. Smith (a major manufacturer of pool ladders and rails) now offers a rubberized coating for pools w/ a SWG. I'll probably replace the ladder and possibly the step rail in my pool in a few years once the rust starts to spread. Right now I'm the only one who notices it and it's a very, very minor nuisance). Note: I can't attribute these minor corrosion issues to the presence of salt.

Re: coping and decking - well, limestone is very, very susceptible to pitting and corrosion, even from spillover waterfall features. I have a concrete deck, and while it's overkill I tend to hose the deck down after alot of splashout.

Tabs and sticks can cause rapid buildup of CYA, which can lock up your effective chlorine, requiring ever higher sanitation and shocking levels. If you decide to do away w/ the SWG, I suggest you use plain old generic unscented 6% bleach to maintain your chlorine levels

*If I understood your post correctly, you are testing your levels through a pool store and test strips. There are brands of test strips that are usually accurate enough for routine maintenance and can indicate balance problems. I won't even begin to try to tell you how inaccurate pool store tests can be, nor describe some of the laughable exchanges I've heard between local pool store employees and unwitting pool owners. If I've learned one universal recommendation from this forum, it is to buy a high-quality test kit, and learn how to test your pool water yourself. I use a Taylor K-2006 and sleep easily at night - my water has been crystal clear the past two seasons, day in and day out. Sorry, I'm too tired to locate links to the pool vendor I buy my Taylor kits from, or the link to another, highly recommended test kit manufacturer, but you can use the advanced search feature on this forum and find those links very easily. You'll soon learn how to test your water within minutes, and also learn that once your levels are within proper range, you really need only test pH and FC on a weekly basis - pH, TA, CH and CYA need only be tested a few times each season (including opening and closing).

[billp]

But I am worried about the aluminum rails and the "coated steel box".... I am thinking of ripping out the SWG ... To cap it all off I read on the one video comment about stainless steel leaching hexavalent chromium in salt water pools. Is this a real cause for concern?

I suspect that if you drink over 200 gallons of pool water the chromium may become toxic...

Here are some observations I have made over the years. In the mid 80's when I started studying chlorine generators, everyone would say oh you don't want to dump all that salt in a pool, bad bad... Then I bought a TDS meter and started testing the commercial pools I was caring for. I was surprised to find that the high use pools, after only one season, had enough salt in them to run a Cl gen (due to salt build up from liquid Cl). Since I did not see the bad things everyone predicted it got me to reexamine the whole issue. Since then the pools where I see significant corrosion have TDS levels well over 5,000. One pool had a TDS of 8,000 and the light fixture brass face rings showed noticeable deterioration compared to others in lower TDS pools. Also at salt levels in the 3,000 range cheap stainless will show deterioration. In the days of mostly stainless steel filters the mfrs all claimed to use the same ss, but something was different because some filters were definitely more sensitive to high salt levels. Using sacrificial anodes I have been able to reduce filter corrosion in many cases to almost zero.

Aluminum does not get along well with pool water. If you leave an aluminum pole in the water overnight you can see definite corrosion in less than a day. On the other hand, I have a customer with a pool cover with aluminum rails which has had a salt pool for years and has no noticeable corrosion. But the pool gets very little use so there is not even much splashing on the rails. I think ripping out the Cl gen may be unnecessary.

As far as the ORP issue, if it was higher after partial drain & refill this could be explained by a loss of CYA. Personally I think an ORP controller in the average residential pool will probably cause more problems than it solves. They are really a high maintenance item compared to most pool equipment. In a commercial environment with lots of supervision they are great, every pool should have them! If you get hung up on the ORP magic number of 650 you will drive yourself nuts. Best way to use it is to get your Cl & pH where you want them then read the numbers on the unit and set the thing to keep them there. Aquasol used this approach successfully for many years and did not even have any output readings on their units.

I have seen stainless steel rails last for decades in low to moderate salt pools with NO noticeable corrosion. And I have seen high priced commercial grab rails on the deck (not in the water) with noticeable corrosion...

Bottom line if you keep the salt level in the recommended range (along with Cl & pH etc) I don't think you will see any noticeable increase in corrosion compared to a "regular" pool.

[quantumchromodynamics]

This sounds like a combination of galvanic corrosion, high chlorine levels relative to the cyanuric acid level and cheap screws.

Stainless steel used around a swimming pool should be type 316. 316 contains molybdenum, which helps the steel resist corrosion in a chloride environment. Any stainless steel used around a pool should be almost completely non-magnetic. The nickel in the 316 stainless steel is what makes the steel almost completely non-magnetic. A strong magnet should be used to test all stainless steel. Any stainless steel that is strongly attracted to a strong magnet should be replaced.

The water is electrically conductive and the salt cell is pushing out electrons into the water and removing them from the water. Most electrons that go into the water connect to hydrogen ions to form hydrogen gas. However, some electrons will inevitably escape to flow through the water.

Most of the electrons that are pulled from the water are pulled from the chloride ions to form chlorine gas, but some electrons will be attracted from the water. The current flowing through the water, combined with dissimilar metals, sets up the perfect opportunity for galvanic corrosion.

[rocket]

Awesome stuff guys. I am printing alot of it out to give to the pool guy.

Two other questions.

#1 I have read somewhere on here that a sacrificial anode works well to stop corrosion. How do you do this? What would it be made out of? I want to stop the corrosion of the screws (hand rails are powder coated) and especially the concrete, but I also have aluminum rails on my automatic pool cover. I think I read something about zinc or magnesium?

#2 The pool guy put something in my skimmer basket (round metal thing) a few weeks ago that he said would help stop corrosion. Obviously it did not work. What is it and should I keep it in the basket?

[ps558]

Awesome stuff guys. I am printing alot of it out to give to the pool guy.

Two other questions.

#1 I have read somewhere on here that a sacrificial anode works well to stop corrosion. How do you do this? What would it be made out of? I want to stop the corrosion of the screws (hand rails are powder coated) and especially the concrete, but I also have aluminum rails on my automatic pool cover. I think I read something about zinc or magnesium?

#2 The pool guy put something in my skimmer basket (round metal thing) a few weeks ago that he said would help stop corrosion. Obviously it did not work. What is it and should I keep it in the basket?

I have heard if the bonding of the pool ladder cups etc can be corroded with SWG if they are bonded all together, but that would have nothing to do with skimmer screws, but maybe the light

[mickey4paws]

Rocket, I would definitely get yourself a good test kit. It really does make a difference to be able to correctly test your own water and not have to depend on the pool store.

Very interesting topic. We just got our SWG this year. I have noticed some rusting on the ladder, where the screws/bolts attach to the ladder's steps. I honestly can't remember if it was there before we got the SWG or not. I have also noticed a couple of small specks of what looks like rust on the bottom of my vinyl liner, close to the area of the ladder. Maybe those specks were also there before and perhaps I just never noticed them. We were previously using Baquacil so this summer is the first time our pool has been really crystal clear and so it's easier to notice things.

I use the TF100 test kit, my last readings:

FC 3.5

CC 0

PH 7.6

CYA 65

TA 100

(didn't do CH test)

Our salt level for most of the summer was 3200. Now it's only 2800 but since we're closing in a couple weeks, we decided not to add any more salt this season.

[quantumchromodynamics]

The pool guy put something in my skimmer basket (round metal thing) a few weeks ago that he said would help stop corrosion. Obviously it did not work. What is it and should I keep it in the basket?

The disc is probably zinc. A sacrificial anode has to be connected to the bonding wire to work properly. Three of the most corrodible metals on the corrosion scale are aluminum, then zinc and then magnesium. A magnesium anode will work better than a zinc anode for protecting aluminum.

Using a sacrificial anode is just trying to suppress or mitigate a problem that should be fixed or eliminated completely. This is something I would consider rather urgent, especially based on the rate of corrosion you are reporting.

One thing at risk is your bonding lugs that connect the bond wire to the steel in the concrete. If they corrode, you can lose the bonding to the concrete, which could cause people to get shocks when getting out of the pool if there are stray currents in the water or grounding system.

You may be experiencing stray currents unrelated to the salt-water chlorine generator. You should have an electrician thoroughly check your electrical and bonding to make sure they are working properly and that there are no stray currents. Be sure that the electrician checks the grounding and neutrals for capacity and stray current.

http://www.pooltool.com/44413Catalog.pdf

http://www.pooltool.com/index.php

http://thepoolbiz.blogspot.com/2007/03/str...lving-your.html

http://thepoolbiz.blogspot.com/2006/10/why...-have-your.html

[chem geek]

Three of the most corrodible metals on the corrosion scale are aluminum, then zinc and then magnesium. A magnesium anode will work better than a zinc anode for protecting aluminum.

You can see from the electrochemical series here that the order from most reactive to least reactive for metals typically found in pools (or sacrificial anodes) is: magnesium, aluminum, zinc, iron, copper. A zinc sacrificial anode connected to a bonding wire with aluminum would help protect stainless steel (which is iron with chromium) but it would not protect aluminum and could even make things worse since it may more quickly react than stainless steel (since it doesn't have chromium oxide passivity layers protecting it).

As you point out, magnesium is what should be used as the sacrificial anode if there is any aluminum connected to the bonding wire.

[quantumchromodynamics]

1) http://corrosion-doctors.org/Definitions/galvanic-series.htm

2) http://www.corrosionist.com/Galvanic_Serie...in_Seawater.htm

3) http://www.corrosionsource.com/handbook/galv_series.htm

4) http://www.engineersedge.com/galvanic_capatability.htm

5) http://www.poolspanews.com/2009/081/081stains.html

These show magnesium, then zinc, then aluminum.

[quantumchromodynamics]

http://www.pennfast.com/design_info/galvanic.html

http://www.mcnallyinstitute.com/04-html/4-1.html

http://www.metal-mart.com/Guides/Galvanic.aspx

http://www.underwater.pg.gda.pl/didactics/...20Site!.htm

http://www.valleyhardware.ca/technical/corrosion.html

[chem geek]

I stand corrected. I was looking at electrochemical potentials of the pure metals, but these do not fully account for passivity layers and standard aluminum has a passivity layer (or is an alloy, so not pure) that retards corrosion just as stainless steel is less corrosive than plain steel. The electrochemical potentials are also with 1 molar solutions not typical in normal water. Also "reactivity" as with acids isn't exactly the same as corrosion from oxidation from dissolved oxygen. Since reaction rates depend on specific chemicals involved, chlorine may react somewhat differently than even oxygen. And it is known that higher chloride and sulfate levels directly affect the passivity layers of some metals, such as stainless steel, more than others (see p. 28 in this file).

This link gives a good explanation of the difference in the electrochemical or electromotive force (EMF) series and the galvanic series.

So that would mean that a zinc anode would probably protect aluminum (one of the sources showed them to be close) but that magnesium would be better (stronger in protection). Thanks for setting me straight.

[rocket]

After reading quantumchromodynamics post and going over to the pool guys blog and reading about stray electiric currents I am officially about freaked out. The pool guy says in one of his blogs something about the Hayword SWG gives off enough volts that theoretically would be enough to cause paralisis or death. That's not exactly what I signed up for. Now is this really possible? Even if the ground wires are heavily corroded and loose they bonding as quantumchromodynamics mentions above.

[chem geek]

The SWG systems use low DC voltages, though ones that use bipolar cells get up to the 25V range, but that's in the cell itself (i.e. across the plates).

What brand of automatic cover do you have?

[rocket]

The SWG systems use low DC voltages, though ones that use bipolar cells get up to the 25V range, but that's in the cell itself (i.e. across the plates).

What brand of automatic cover do you have?

So your saying that voltage is to low to hurt anyone?

Leading Edge by Fort Wayne Pools

[chem geek]

What I am saying is that you aren't putting your hands inside the cell with one hand grabbing one plate and the other grabbing the other. The only way this voltage would be a problem for shocking is if there was a short somewhere that connected an active voltage to the bonding wire AND that bonding wire was not grounded (this varies by jurisdiction in terms of whether the bonding wire is grounded) AND you touched a metal component in the pool along with being grounded elsewhere. Of course, any of the components with much higher voltage, such as the 220V pump, could likewise short to the bonding wire, but in practice you don't see this sort of thing happening.

People sometimes report tingling in some pools and a pool with more salt in it will be more likely to have this occur (due to the greater conductivity), but the source has to do with stray voltages usually associated with improper neutral grounds in the main (i.e. house) electrical system, sometimes with a neighbor. A nice simple summary of the source of these stray voltages and currents is here. My utility has a document about this here. Though SWG pools aren't the source of such voltages, the extra conductivity of the water due to higher salt levels increases the amount of current for a given voltage so can increase the amount of shock.

Of all the things to worry about with an SWG pool such as corrosion of metal, deterioration of permeable stone, explosion of the cell if the safety shutoff fails, etc., electrocution is not one of them. Most people that have SWG pools love the convenience and most don't have problems, but as you can see from reported incidents there are serious issues with some pools. The water, after all, is more salty than most non-SWG pools and that salt can get splashed out and is more conductive for galvanic corrosion. So any "on the edge" metal components would be more susceptible (especially steel in diving board mounts or in furniture or inexpensive bolts in Intex pools) as would soft stone (some limestone and flagstone). If the pool has high salt levels but doesn't use CYA in the water, as with most indoor pools, then the chlorine is far more reactive so can accelerate corrosion (one user reported serious stainless steel corrosion in less than a year, but had 3-5 ppm FC with no CYA). Indoor pools should use a small amount of CYA (around 20 ppm with not more than 4 ppm FC normally).

As for your pool cover, check the manual that came with it to see if there is any warning in it about galvanic corrosion occurring when the system is used in a saltwater chlorine generator pool. Some covers are not warrantied against galvanic corrosion.

When I asked my own pool builder if he saw any corrosion problems with SWG pools (which are the vast majority of his new installs), he said that the only problem was with automatic pool covers, especially those that had their aluminum leading edge bar dipped in the water as with "vanishing"-style covers. The solution the manufacturer recommends is to use a sacrificial anode and he hasn't found problems since.

[rocket]

Thanks Chem Geek you are an amazing fountain of knowledge. My pool guy actually already has a sacrificial anode on order. He called around and apparently our State Inspectors for pools (whoever that is) recommends or requires them for SWG pools. Not sure if it is zinc or magnesium though.

Another question. Daughter had B Day party today kids playing everywhere and my son dropped his battery powered car in the pool. It was probably on the bottom about a minute before my wife got it out. When I took the batteries out to replace, one of them was split open on the back end. The toy no longer works, no big deal, but wondered if the battery could have leached mercury or nickel or something harmful into the pool. I admit I am a paranoid person.

[chem geek]

This sounds like a standard battery that is either carbon-zinc or alkaline and is a combination of solid zinc with powdered carbon and solid manganese(IV) oxide (manganese dioxide). The electrolyte is either a combination of acidic ammonium chloride and zinc chloride ("Heavy Duty" batteries are mostly zinc chloride for the electrolyte) or alkaline potassium hydroxide in alkaline cells.

The manganese(IV) oxide is an oxidizer, but weaker than chlorine and I'm not sure what would happen to it in pool water. The powdered carbon is innocuous. The solid zinc will also get oxidized to zinc ions and the zinc chloride also adds zinc ions with the biggest problem there being staining, but that is unlikely given the small amounts we're talking about. The ammonium will lower the pH while the hydroxide will raise it, but by such small amounts as to be negligible. The ammonium will also get oxidized by chlorine to nitrogen gas and is essentially like the ammonia from your sweat and urine so not a big deal.

So other than a small consumption of chlorine to oxidize various substances, the only real side effect is the leftover zinc ions and that's not enough to be worried about and the manganese oxide which is probably in small enough quantities to not be a problem since you don't drink large quantities of pool water anyway.

[Pool Clown]

IMO, Those things are so darned finicky (industry term), that if they were to get even remotely close to doing any of the things discussed so far, that they would shut themselves off.

[rocket]

thanks. it was just your run of the mill double AA energizer battery

[rocket]

does anyone have a link to where you can buy a sacrificial zinc or magnesuim anode?

[rocket]

Got all chemicals added, but for some reason it seems no matter how much PH I add it always seems low. Computer print out tells me exactly how much to add, but next time they test it is still low. Any ideas? When you add stabilizer (CA) would this cause PH to go down for some reason?

[chem geek]

Adding stabilizer to increase the CYA level by 30 ppm would lower the pH from around 7.5 to 7.1 and depending on how you added it, it can dissolve slowly. If you added it to the skimmer to get caught in the filter, then it can take up to a week to dissolve. If you put it in a sock or panty hose and hung it over a return flow or if you put it in a T-shirt or skimmer sock in the skimmer, then it can dissolve in 8 hours or so.

Usually, a fairly fast drop in pH would occur from using Trichlor pucks/tabs. If one had chlorine usage of 2 ppm FC per day, then Trichlor would have the pH drop from 7.5 to around 7.0, assuming no outgassing of carbon dioxide. It would have the TA drop by 10 ppm in that same 1 week period.

[rocket]

That would explain it. Also ever since adding the round of Calcium and PH last time I have a white powdery material on the bottom of the pool that won't sweep up or dissolve in the water. Not sure how to get rid of it.