New Member Question: Is the salt from bleach or sodium hypochlorite harmful?

[dmeyer]

I found myself an accidental pool owner after buying a house with a really beautiful 30k gallon kidney shaped pool with a mechanized retractable cover. Chemically, the pool appears to be a great shape, and we had a pool guy out who verified that right now things look good.

The posts here have be been invaluable in seeing that the costs of this thing and the work involved is going to be manageable. I'm signing up in anticipation that I will have lots of questions, once i get my test kit up and running. Until then the information in the forum seems quite complete, and the BBB method advocated here makes a ton of sense.

Here's something I haven't seen addressed yet. My understanding of Sodium Hypochlorite (e.g. bleach, liquid "shock") is that it will break down in order to chlorinate my pool, with the only side effect being some added salt. My question is - How is it that the salt is harmless? Salt is hard to filter from water, so it seems like this could build up. If I really use my imagination, I wonder if my pool could ever get salty enough it could start to corrode the metal mechanism on my cover. I'm sure there's no basis to this, because I know lots of people use sodium hypochlorite, and I've never seen a complaint, but is it possible this could become a problem? Any idea why not?

[PoolDoc]

Salt is not harmless, absolutely. It's just harmless compared to your other options. By the way, all forms of chlorine ultimately add salt, as Cl+ (oxidizing form of chlorine) becomes Cl- (salt). Bleach just includes salt, besides the oxidizing form of chlorine.

And yes, salt can corrode all forms of metal, if it's high enough -- including cover mechanical parts.

But, we wouldn't necessarily encourage people with 30K gallon pools to use bleach as a sole source of chlorine, long term. We just usually recommend it, on first contact with a new pool owners, since it's unlikely to make a pre-existing condition much worse. By contrast, adding cal hypo to a pool with high Alk and high Calcium can turn a pool milky looking, and using dichlor on a pool with high stabilizer can make a high CYA level higher.

[dmeyer]

Interesting, thanks for your reply. I look forward to getting some real numbers from the water.

[chem geek]

As a point of reference, I use 12.5% chlorinating liquid in my pool as my primary source of chlorine. I have relatively low daily chlorine demand of 1 ppm FC per day due to a mostly opaque electric safety cover, though the pool is used (open) every day for an hour or so and longer on weekends and it's kept warm at 88ºF. The point is that salt does build up so I use winter rains to dilute my pool water by up to 50%. It's a nice way of refreshing the water to get rid of anything in it that isn't handled by other means such as filtration or oxidation. My salt level tends to range between 600 and 1200 ppm as a result.

A more typical daily chlorine usage for pools without opaque covers is around 2 ppm FC per day and at that rate one would add about 100 ppm salt per month if there were no water dilution.

For those in areas of the country with summer rains, that can also be used to help with diluting the water if it's enough to overflow or if one intentionally drains some (having summer rains just make up for evaporation won't change the water chemistry).

Note that saltwater chlorine generator pools have 3000 ppm salt which is generally higher than most manually dosed pools that are usually in the 1000-2000 range, though obviously it depends on actual chlorine usage, length of season, and amount of water dilution.