SWG with liner type indoor pool.

[chem geek]

I am no expert in corrosion, but have stumbled upon some people who have been saying that SWG pools are a much bigger problem than non-SWG pools. This link is to a blog that has some photos of corrosion and some speculative theories as to why. I've also started this thread in The China Shop to talk about these issues, speculate on what's going on and solutions, and eventually come to some consensus that can be presented to this general forum.

Generally speaking, all metal parts touching the water in a pool are supposed to be connected together with a "bonding wire" that makes sure there is no potential difference between them. This is not connected to "ground" partly to avoid stray currents developing from other electrical items connected to ground, but I saw reports of possible small shocks with the traditional bonding wire approach and that some jurisdictions were considering adding a requirement to connect the bonding wire to a wire mesh in the hardscape and coping near the edge of the pool. At any rate, I do not believe that the corrosion is due to the bonding wire and galvanic corrosion, but you should be able to very easily determine that by disconnecting the wire from the rusted component and insert a current meter between the wire and the rusted metal component. If you do this, let us know what you find out as this would be helpful in determining what is really going on.

My hunch is that it is the saltier water that is causing greater rates of corrosion. There are different grades of stainless steel and some are resistent to salt water while others are not. So I believe it's a combination of the salt water plus inferior (for the salt environment) stainless steel (see this link for a Wikipedia article on Stainless Steel and note the difference between Types 304 and 316 as well as the discussion on Pitting Corrosion). I doubt that grounding will help, but you can certainly try 1) grounding one component, 2) disconnecting the bonding wire from another, and then see which does better.

Perhaps others with more experience and knowledge in this area can be more helpful.

In my own pool, which is not SWG, I had some rusting in the steel mountings of stainless steel bars, but this was only where Trichlor in a feeder "parked" itself as I had tethered it to one of the bars. The acidity from the Trichlor was the more likely culprit in this case and needless to say, I don't use Trichlor anymore (also because I ended up with over 100 ppm CYA).

Richard