Swg Decision

[dubele]

Hi,

I am still trying to decide on my brand new, yet to begun construction, gunite in ground pool on whether to go with salt or chorine for sanitizing. I was leaning towards salt, but maybe I am reading too much. I am hearing great things about maintenance, but I have read the following negatives:

1) It is more corrosive than chlorine and you have to make sure EVERYTHING is non-corrosive and salt "compatible".

2) For new gunite pools, salt will not allow the concrete to cure properly.

3) For waterfalls/decents, you have to make sure the salt won't damage them.

4) The salt gets in the "atmosphere" and corrodes everything.

5) If you don't use muriac acid to lower the PH, you increase the corrosive effects.

There are a few other things I read.

A piece of me says, go with chlorine as it is "tried and true". The other side of me says, salt is the way to go...and I have a friend who converted and is very happy. I just worry about corrosion of the plaster, stamped concrete deck, equipment and pipe joints.

If you have real life experience of over, say, 7 years with a salt system, I'd love to hear from you. If you are in the pool industry, I'd rather you keep your sales pitches and lying to yourself.....you are the folks who made my whole process of getting a new pool a confusing mess.

Thanks,
Doug

[chem geek]

I don't have an SWG myself but have read the experiences from hundreds (if not thousands) of SWG pool owners so can give you the straight scoop:

1) It is more corrosive than chlorine and you have to make sure EVERYTHING is non-corrosive and salt "compatible".

Partially true. Higher salt levels are more corrosive or problematic in three ways.

First, the higher salt level increases water conductivity which increases metal corrosion rates. This can be easily mitigated by adding a zinc sacrificial anode buried in moist soil and connected to the bonding wire. Or you can use titanium or curpo-nickel in the gas heat exchanger instead of copper (though that doesn't often corrode, but sometimes does). The most common corrosion is seen with aluminum header bars in vanishing electric safety covers (since the aluminum is immersed in the water in this case) and the use of an anode prevents this corrosion.

Second, the higher chloride level increases the rate of corrosion of stainless steel in particular since it interferes with the reformation of the passivity layer. Most pools already use higher quality corrosion-resistant stainless steel so are not affected, but inexpensive above-ground pools such as some Intex pools, may use components using inferior stainless steel that are more susceptible to faster corrosion. They will likely corrode in regular water as well, but will just take longer. Some of these pools even have zinc components (screws) which is ridiculous.

Third, the higher salt level that splashes out can be a problem for soft stone if there are repeated splash-out and evaporation cycles. So this is more of a problem where soft stone is used, where there are not regular summer rains to wash away the salt, and where the air is hot and not too humid so that evaporation occurs. This combination occurs in some areas of Texas where most of the problems with stone deterioration have occurred, but it also occurs in some desert areas as well. It generally isn't seen in Florida where it regularly rains and is humid and not so much in the Northeast either.

2) For new gunite pools, salt will not allow the concrete to cure properly.

Though this may be true, one does not add salt to a newly plastered pool. One generally waits at least 30 days and the plaster will be essentially cured by that time. So this is a non-issue.

3) For waterfalls/decents, you have to make sure the salt won't damage them.

This is basically the same as #1 regarding salt splash-out. Salt won't be a problem where the water is flowing, but around the edges where splashed and evaporated and again it depends on the type of stone that is used.

4) The salt gets in the "atmosphere" and corrodes everything.

That simply isn't true unless you have a mister or fountain using pool water. Instead, what is more likely is that you carry-out the saltwater in your bathing suit and drip it so that can corrode chairs and chez lounge and diving board mounts if these have exposed metal. This happens anyway in a regular pool as well, but the corrosion takes longer when the salt levels are lower. A non-SWG pool often has salt levels in the 500-1500 ppm range and sometimes 2000 ppm so it's not as if we're talking about being 10 times more corrosive, but even a factor of 3 can be noticeable to people (the difference between 3 years and 9 years, for example).

5) If you don't use muriac acid to lower the PH, you increase the corrosive effects.

That doesn't make sense. The pH in SWG pools does tend to rise, but there are ways to reduce that rate of rise. A higher pH is not more corrosive, but can lead to calcium carbonate scaling, especially in the SWG cell, but again this can be avoided by proper water chemistry -- a lower TA level, higher CYA level (for lower SWG runtime) with appropriately higher FC level, and 50 ppm Borates.

[dubele]

Thanks chem geek for the reply and your time

[dubele]

So, could I use the SWG system, but just treat my pool as if it was a chlorine pool? Meaning of the 3 types, salt, chlorine, minerals.....I would just add chlorine and do the same with all other chemicals as if I had a chlorine pool. I will check with my builder and see what he does as far as when he adds salt.

[chem geek]

A pool with an SWG system IS a chlorine pool. It is a saltwater chlorine generator. There are not 3 types of pools -- "salt" and chlorine are both chlorine pools unless "salt" means a pool using ocean water that is not disinfected with chlorine. Using minerals is not recommended since they can stain pool surfaces and copper can turn blond hair green and they are not fast-acting disinfectants.