Chlorine Options?

[u078356]

We are starting to plan for a pool. One area in which I have questions is what option is best for cleaning the water. I have done some more research on pool cleaning technology (I know, a little knowledge in the hands of an amateur...).

One major manufacturer of pools opts for an Ozone generator to oxidize non-living waste. Then, they combine this with a chlorine release system (chlorine tablets in an automated dispenser). This provides the sanitizing capability. The overall amount of chlorine needed is reduced since the ozone is oxidizing the non-living waste more effectively than chlorine. Also, the ozone works better with spa water since chlorine loses its effectiveness in high temperature applications.

In essence, this combination decreases the amount of chlorine required and eliminates dumping bags of salt into the pool.

A concern with the chlorine generator approach that I have read is that the NaCl saturation of the pool, even if limited, has an impact on the tile and pool finish. Also, the salt to chlorine process is relatively slow--2-3 days--so a homeowner may overcompensate, adding too much salt in order to get a change, contributing more to the effect on the pool finish. Then, when the excess salt hits the monitoring system, it is interpreted as too high, shutting down the generator, which then leaves more salt in the water--starting a cycle.

I can see some sense to the ozone approach. It seems to be overall lower cost of ownership than even the chlorine generator: the UV ozone generator uses low power, has a long source life span, reduces the need for additional chemicals to consistently maintain appropriate pH balance with the salt being added.

Question: does this make sense? Is there a consensus in the pool world as to the best set up for a low-maintenance cleaning technique? Chlorine Generator alone? Chlorine Generator with Ozone Generator? Chlorine dispenser with ozone generator? Chlorine dispenser alone?

Another question: has anyone else heard about problems of the salt which is added to the pool attacking the tile or pool surface?

Thanks for any insights you can provide.

David

[waterbear]

Ozone distroys chlorine and chlorine destroys ozone. It is important to maintain a minumun of 2 ppm free chlorine in the water at all times. You chlorine usage with ozone might actually be higher than without to maintain this minumum level. Also, ozone leads to the increased formation of chlorates in water sanitized with chlorine (and to bromate formation in bromine sanitized water) Chlorates and bromates are considered to be harmful disinfection byproducts (bromates are a suspected carcinogen). Residual santizer is necesary in pool water and ozone had no residual (nor should it in a properly operating system since it is toxic.) As far as a tablet feeder---you would be using trichlor which is stabilized chlorine. What type of filter are you considering? Trichlor is not a good option with a cartridge filter, especially in any areas of the country with an extended swim season because your cyuauric acid levels will rise too high quickly and you will have to drain and refill to lower them. Even with a sand or DE filter this does occur but not as quickly. A salt water generator is the way I would go. The salt level does not have to be ajusted very often. Most of the units on the market run at about 3000-3500 ppm which is barely perceptible but it does increase the comfort of the water considerably since it is closer to the isoelectric point of the human body.Biggest drawback to a SWG is increased acid usage but that can be minimized by 'tweaking' your water balance.

There have been some instances of corrosion reported with SWGs when cheaper materials are used in the pool construction. If you pool is constucted to withstand a seaside environment then there should be no problems. Certain decking and coping materials such as limestone do need to be properly sealed. There is actually more risk of plaster damage from high levels of cyanuric acid in the water than from salt. With a SWG the cyanuric acid is added to the proper level and does not continue to rise as it will with trichlor.

SWGs maintain an even chlorine level in the pool with minimal user intervention and the majority of pools with SWGs rarely develop any combined chloramines and therefore do not need to be shocked. You do not need to keep adding salt to produce chlorine unless water is lost from the pool by filter backwashing, spashout, or a leak. Ditto for the cyanuric acid.

IMHO, there is no advantage to putting an ozone unit on a residential pool and it may actually complicate your pool maintenance. If you are looking at one of the units that says it can be used with lower free chlorine levels than without that is rubbish. The minimum residual chlorine of 2 ppm is NECESSARY to properly sanitize the water.

[chem geek]

Just a couple of additional comments. If you have an outdoor pool that is exposed to sunlight, then the amount of combined chlorines and disinfection by-products you will get will be minimal. With a salt-water chlorine generation (SWG) system, they will be virtually nil. For an indoor pool or a pool not exposed to sunlight then using an ozone system to oxidize organics is more reasonable, but even then you can use a weekly maintenance dose of non-chlorine shock (potassium monopersulfate, KMPS) instead.

You could also use an SWG system indoors, but need to make sure to use Cyanuric Acid (CYA) in the pool even though it is indoors. The CYA will reduce corrosion rates for metal from the chlorine in salt water.

You should keep in mind that in a pool with Cyanuric Acid (CYA) in it, the amount of disinfecting chlorine in the pool is very low and the production of disinfection by-products is also very low. All reports of asthma and respiratory problems with competitive swimmers and small children have been with INDOOR pools and such pools are not exposed to sunlight and have no CYA in them (and have poor air circulation) even though they probably should (have CYA in them, that is, but the industry currently just thinks that CYA is only useful to protect chlorine destruction from sunlight).

[u078356]

Thanks for the detailed feedback so far.

I have found that one of the concerns in our area (Texas Gulf Coast, south of Houston) is the source of rock and/or flagstone used around pools. Evidently, the salt water levels when a salt water generator is used have been shown to erode the rock. This problem is not so evident in other areas of the country where the decorative rock is not as porous.

To create a "soft water" feel without the use of a SWG, one manufacturer is using "Borax" as an additive. Then they use a ozone generator and the automatic chlorine dispenser. I was told that this combination works so effectively that there is minimal need to ever shock the water.

It sounds like this debate is currently quite polarizing to the pool manufacturing community.

David

[waterbear]

Thanks for the detailed feedback so far.

I have found that one of the concerns in our area (Texas Gulf Coast, south of Houston) is the source of rock and/or flagstone used around pools. Evidently, the salt water levels when a salt water generator is used have been shown to erode the rock. This problem is not so evident in other areas of the country where the decorative rock is not as porous.

To create a "soft water" feel without the use of a SWG, one manufacturer is using "Borax" as an additive. Then they use a ozone generator and the automatic chlorine dispenser. I was told that this combination works so effectively that there is minimal need to ever shock the water.

Borates in a 30-50 ppm concentration will reduce santizer demand (you still need to maintain the same residual) by acting as an algaestat. They also help to stabilze pH. It is not necesary to use the expensive pool store products to to this. You can use borax from the grocery store. They are both sodium tetraborate. The only differenece between the pentahydrate form you buy from the pool store and the decahydrate from sold in the grocery store is the number of water molecues attached so you would need slightly more of the decahydrate to achieve the same 30-50 ppm level. If it were my pool I would investigate other decking material instead of natural stone and go with the SWG AND add the borates!

It sounds like this debate is currently quite polarizing to the pool manufacturing community.

David

Hope this is helpful.

[randy]

I agree with everything said, with one small addition flagstones and limestone dissolve/chip period salt system or not. At least here in the SoCal area. I have no idea why they're getting so popular around pools. I also wouldn't waste my time with ozone unless I had a lightly used covered pool with an oversized ozone system, contact chamber the works.