Switching from Chlorine to SWG

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Visitor

Switching from Chlorine to SWG

Postby Visitor » Tue 16 Dec, 2008 19:02

We're planning to switch from chlorine/acid to SWG/acid for pool sanitizers.

Now, I'm new to this whole pool maintenance position, serving a retirement home of about 250 residents, and an apartment block of similar size.

I'm told SWG will be easier to manage, more reliable, and eliminate issues of "hazardous" chemical. Agree?

Any downsides?

I've been all over the internet the last 2 months training myself on pools generally, pool chemistry, and on our current chlorine system. Now I get this SWG wrinkle tossed in!

I don't expect any big "re-education" in the chemistry, but I'm less certain about the impact on all the filters, heaters and plumbing for the pool and the hot tub. All facilities are indoor, eastern Canada. Equipment ranges in age from cast iron pipes for deck drainage (about 40 years old), to seemingly "recent" filtration and heat exchangers (certainly nothing newer than 5 years. [Staff and management turnover leaves me no-one to turn to for history of the hardware.])

Any "heads up" warnings?

Thanks, for any thoughts!

Ike


chem geek
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Switching from Chlorine to SWG

Postby chem geek » Tue 16 Dec, 2008 21:19

What type of chlorine were you using before? Since you said chlorine/acid, I assume it was a hypochlorite source of chlorine such as Cal-Hypo or chlorinating liquid (sodium hypochlorite). You shouldn't have needed to add very much acid when using a hypochlorite source of chlorine. If you were, then that means your Total Alkalinity (TA) was too high.

An SWG will tend to make the pool rise in pH even more than your use of hypochlorite. Some of this is due to the greater aeration from the gas bubbles, but some is due to undissolved chlorine gas outgassing. You can reduce the former effect by lowering the TA. The latter effect may be reduced if the pipe run between the SWG and the pool is long and the returns are not pointed up. You can also reduce the rate of pH rise by using 50 ppm Borates in the pool as this acts not only as an additional pH buffer, but also as an algaecide letting you turn down the SWG on-time. Also, you can operate at a higher 70-80 ppm CYA level with a target FC of 4 ppm as the higher CYA level will reduce the loss of chlorine from sunlight. This assumes a light bather load at the pool. If the bather load is heavier, then more chlorine will be lost from the heavy bather load than from sunlight so the higher CYA would not help in that case.

Finally, the higher salt levels will be more corrosive. As to whether this is a problem, that depends on the materials used in your pool. If it's on the edge, there can be more problems show up. The worst is with aluminum tracks for covers with splashed out water where evaporated salt accumulates. Next is aluminum headers of pool covers if immersed. Any galvanized or zinc items would corrode faster as well. Copper heat exchangers may corrode faster though this is less definite. Steel items such as under diving boards or in chez lounge chairs may corrode more quickly from dripped water. Worst case scenarios are described in this link , but realize this is not unbiased. Most people with SWG pools love them and don't have serious problems. If you have known possible areas where metal can corrode, then this can be partially mitigated by using a sacrificial anode, usually attached to the bonding wire. This can be a zinc block unless any aluminum is present in which case a magnesium block must be used.

You can learn more about taking care of water balance with an SWG here at the Pool School at Trouble Free Pool.

Richard
micahharwell
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Switching from Chlorine to SWG

Postby micahharwell » Sun 11 Jan, 2009 13:20

chem geek wrote:Copper heat exchangers may corrode faster...


Most new pool heaters can be configured with cupronickel heat exchangers that are more resistant to salt water systems. They add $150 to $400 to the price of the heater, depending on the size.
chem geek
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Switching from Chlorine to SWG

Postby chem geek » Mon 12 Jan, 2009 00:17

Yes, any of the issues with the higher salt levels can be mitigated. Heat exchangers can use cupro-nickel or titanium. As I had mentioned, the bonding wire can have a buried sacrificial zinc anode for protecting stainless steel and other metal, though if there is any aluminum then a magnesium block should be used instead. This is done, for example, to protect aluminum headers in automatic pool covers, especially if they are "vanishing" covers where the header is immersed in the water. Stone coping can be sealed and any splashed-out salt can be hosed away.

Most people are happy with their SWG pools, but one should understand the pros and cons and the risks that can be mitigated.

Richard

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