Corrosion in swimming pools

[Dannie Boy]

Has anybody experienced corrosion of stainless steel steps in a salt-water swimming pool and if so any suggestions for how it can be prevented? It has been suggested that sinking a couple of copper spikes into the ground and connecting a copper cable to the two fixings on the handrails might do the trick - confirmation that this might work or any alternative suggestions gratefully received.

[Nereus]

It is more likely to be the local use of low grade "stainless steel" that is the problem, some of the rubbish will corrode in fresh water!
It is possible to get 316 grade, or marine grade quality, but as with a lot of things, the cheaper path is taken.

[Dannie Boy]

It is more likely to be the local use of low grade "stainless steel" that is the problem, some of the rubbish will corrode in fresh water!
It is possible to get 316 grade, or marine grade quality, but as with a lot of things, the cheaper path is taken.

Thanks Nerus, I have no idea what grade it is - I will ask but not sure whether I will get a truthful answer or not?

[H2ODunc]

As said DB just low grade stainless steps. Also when people say it is a salt water pool it just means they use salt to create the chlorine to chlorinate the pool and it isnt actually salt water

[Dannie Boy]

As said DB just low grade stainless steps. Also when people say it is a salt water pool it just means they use salt to create the chlorine to chlorinate the pool and it isnt actually salt water

I understand what you say about the salt being used to create chlorine but the water does taste slightly salty, which I guess is no surprise seeing that they put a tonne of the stuff in the pool (20x50 kg bags). By the sound of it though, the cause of the rust is very likely to be "low grade" SS, although not being an engineer, I am surprised at the speed in which the rust has appeared - just 5 days!! Anybody have any thoughts about using the copper spikes/cable - is this likely to work?

[PeteC]

As said DB just low grade stainless steps. Also when people say it is a salt water pool it just means they use salt to create the chlorine to chlorinate the pool and it isnt actually salt water

It is Dunc, but not high concentration salt water. When the chlorine breaks down by sun/human bodies swimming etc., it turns back into sodium chloride and subsequently back through the electrodes once again to be turned into chlorine again. That constant cycle is why a dozen or less 25kg bags of salt will last months for a normal size pool. I read somewhere that the normal salt water pool is about 1/3 the salt concentration of the sea. Almost undetectable, but you can taste it slightly. Pete

[PeteC]

Holy cow Dannie, how big is your pool to need that much salt. Mine is 10 x 7.5/8 meters and the above formula I posted is the initial charge when new water is introduced at pool filling. It will last about 3 months and then I usually need to add one 25kg bag per month to keep it balanced. Perhaps they're selling you salt you don't need, and your concentration in the water is way too high. Too much salt could be the cause of the SS problem. Pete

[Dannie Boy]

Holy cow Dannie, how big is your pool to need that much salt. Mine is 10 x 7.5/8 meters and the above formula I posted is the initial charge when new water is introduced at pool filling. It will last about 3 months and then I usually need to add one 25kg bag per month to keep it balanced. Perhaps they're selling you salt you don't need, and your concentration in the water is way too high. Too much salt could be the cause of the SS problem. Pete

It is 12x7m and it was a new fill, but by the sound of it a bit more than was necessary. I have just bought a test kit so will check it this afternoon and see what results I get. BTW, they were probably 25 kg bags, but definitely 20 of them

[PeteC]

Don't be shocked if your PH alkaline is off the charts. Mine always is and I think you would need to add gallons and gallons of acid to get it within normal range. It's a question I've never asked the experts but IMO you'll never get the PH alkalinity/acidity in balance with a salt water pool. I've never had problems with eye burn, water colour or anything else by leaving it alone as it is. Pete

[Dannie Boy]

Don't be shocked if your PH alkaline is off the charts. Mine always is and I think you would need to add gallons and gallons of acid to get it within normal range. It's a question I've never asked the experts but IMO you'll never get the PH alkalinity/acidity in balance with a salt water pool. I've never had problems with eye burn, water colour or anything else by leaving it alone as it is. Pete

The ph certainly was very high and looks about 8.0 or even slightly higher according to the colour, whereas the chlorine level and bromine were very low and hardly registered any colour at all. I have some chlorine to add, so will do that in small quantities until I can detect a change in the reading.

[Bristolian]

As to the question of the OP, against all that we believe, stainless steel will corrode given the right circumstances (salt water and an electrical current which is generally present in a saline solution with metals present i.e. a low voltage battery).

I remember, too long ago, whilst an apprentice, conducting an experiment where a small plate of stainless steel was immersed in a salt water bath with a rubber band (elastic band) placed around the plate. 3 months later the elasticity or the band, excluding most of the oxygen, caused the rubber band to eat its way through the stainless plate. The solution was to fix a sacrificial metal to the stainless. (Any good electrical conductor will do but for practical purposes copper would be the easiest and most cost effective)
Fixing a piece of copper to the underside of the steps should solve the problem. Over a long period of time the copper will corrode/erode and leave the stainless steel as original.

[Nereus]

Anybody have any thoughts about using the copper spikes/cable - is this likely to work?

To have corrosion caused by electrolysis there needs to be an electrical potential difference between two dis-similar materials, which will lead to one of them giving up electrons and so cause corrosion, or sometimes erosion. With a salt water chlorinator there is a good possibility that there may be stray currents floating around the system, but I doubt very much if grounding the steps would have any advantage. The usual way to overcome electrolysis is to bond the two offending pieces of material together, thereby eliminating any potential difference between them.

[PeteC]

Don't be shocked if your PH alkaline is off the charts. Mine always is and I think you would need to add gallons and gallons of acid to get it within normal range. It's a question I've never asked the experts but IMO you'll never get the PH alkalinity/acidity in balance with a salt water pool. I've never had problems with eye burn, water colour or anything else by leaving it alone as it is. Pete

The ph certainly was very high and looks about 8.0 or even slightly higher according to the colour, whereas the chlorine level and bromine were very low and hardly registered any colour at all. I have some chlorine to add, so will do that in small quantities until I can detect a change in the reading.

When the salt first went in, the water should have turned green. This shocks a lot of people but is normal at the beginning. You need to run the filter constantly for about 2 days, then go back to the normal schedule you use to keep the water properly filtered. That schedule will be longer run times to produce enough chlorine than with a normal chlorine pool. My difference went from 6 hours to about 9 daily. If you increase your run times, your testing for chlorine should reach normal without any need to supplement with powdered chlorine.

The beginning is also the proper time to dump in about 5-6 gallons of acid. This helps stabilize everything and also in getting rid of the initial algae the salt is causing.

It sounds as if you're beyond all of that already, but when I put in a bag of salt every month I also put in about 2 quarts of acid to help things along. Again, not enough to get the PH in balance, but enough to give the pool a nice crystal clear appearance, and no eye burn.

Another thing I blame on the salt system, I tend to get salt deposits on the grout line recesses on the tile. Especially true in 90 degree angled corners. As mentioned the chlorine turns back to salt when it decays. On it's way back through the system to be turned into chlorine again, it seems it likes to seek refuge in the grout recesses. Nothing I've been able to do to stop it except to brush monthly. Never had the problem with my normal powder/tablet chlorine pools before. Pete

[Nereus]

but when I put in a bag of salt every month

I thought that you were using chlorine, Pete? I seem to remember you writing about buying the stuff.

[PeteC]

but when I put in a bag of salt every month

I thought that you were using chlorine, Pete? I seem to remember you writing about buying the stuff.

I was as I got tired of lugging salt bags around. Went back to salt a few months ago simply because once you get it right, you can forget about it, including testing more than once every few weeks. The little one was complaining of eye burn with the powder as well. Stay tuned, when the mood hits I may switch again...or when the salt supplier doesn't want to drive all the way out here. Pete