I'm installing a SWG on a 10K Gal pool / spa combo soon. The customer is also considering Ozone and she's asked me
Any suggestions one way or the other, comments, thoughts, concerns are most welcome.
Florida Leisure Pool & Spa
The use of 50 ppm Borates are usually beneficial, especially in an SWG pool, because they are a strong pH buffer especially suited to slow down a rise in pH. By itself, this doesn't change the amount of acid that needs to be added, but it does allow one to add acid less frequently. The pH buffering also helps reduce scaling in the salt cell because it limits the amount of pH rise at the hydrogen gas generation plate.
The algistatic properties work best against green algae, which is the most common type, but if the proper FC/CYA ratio is maintained then this really just acts like insurance more than anything else. For an SWG pool, the FC should be at least 5% of the CYA level. Also, the CYA level should usually be close to 80 ppm to reduce chlorine loss from sunlight (assuming this is an outdoor pool exposed to sunlight) so this implies an FC minimum of 4 ppm to prevent algae growth.
You can add the 50 ppm Borates in different ways. The least expensive (unless you are buying commercial quantities or products at wholesale) is a combination of 20 Mule Team Borax with Muriatic Acid. Alternatively, you can use boric acid which is close to pH neutral (it's only slightly acidic). You can use The Pool Calculator to calculate dosages and should read Water Balance for SWGs (note how a lower TA target can significantly help reduce the rate of pH rise AND lower the amount of acid you need to use). Unless you have a wholesale source (say, for ProTeam® Supreme Plus), you can buy boric acid at The Chemistry Store or at AAA Chemicals.
An ozonator is not usually of much benefit in an outdoor residential pool because the low bather load doesn't require supplemental oxidation. The chlorine in the pool reacts with the bather load before it even reaches the ozonator via circulation and the hydroxyl radicals from the breakdown of chlorine in sunlight help oxidize the chemicals that are normally slow to get oxidized by chlorine (such as urea). Ozone reacts with chlorine to form chloride and chlorate so in pools with low bather load an ozonator can actually increase chlorine usage, though usually residential pool ozonators are woefully undersized so no difference is seen at all. In residential spas, an ozonator increasing chlorine demand is clearly seen if a spa is used infrequently, such as once a week or less while in a heavily used spa used every day or two the chlorine demand is lowered since in that case ozone can oxidize bather waste so that chlorine doesn't have to. This is why ozonators are very useful in commercial/public pools since they typically have high bather load. They can also be useful in indoor pools due to the lack of sunlight though usually UV is used instead.
Hi Richard, the following is an extract for the European regulations;
On 18 June 2010 the European Chemical Agency added boric acid and borax to the candidate list of ‘substances of very high concern' for authorisation.1 That decision came because they are considered as substances Carcinogenic, Mutagenic or Toxic to Reproduction (CMR), as category 1B reproductive toxins in Europe's Classification, Labelling and Packaging (CLP) regulations.2Thanks to their CMR status, since December 2010 preparations containing 5.5 per cent or more of free boric acid or 4.5 percent or more of anhydrous borax must be labelled: "May damage fertility. May damage the unborn child"3. From June 1 2015, that labelling will have to include the "exploding chest" pictogram for target organ toxicity4.
Boric acid, or related borax products, ingested directly are toxic at higher levels. That is true for a lot of pool chemicals, including various forms of chlorine. I've written details about borates in a thread called Are Borates Safe? In that thread, there are links to the various reports where you can see that the main reason for concern with the concentrated chemical is that the No Observed Adverse Effect Level (NOAEL) was 8.8 mg/kg/day in dogs and as you'll note the first symptoms at higher doses were low testicle size in such male dogs. The reason the limits are "per day" is that, unlike insects, mammals are able to remove borates from the body at a certain level since it is found in the environment including in food. It is when one overwhelms such normal removal rates where one runs into trouble if levels get too high and in such studies the exposure was long-term (i.e. over months).
The oral LD50 is in the 396-699 mg/kg range in mice and rat studies. So for a 60 kg person a fatal one-time dose for half the people would be around 24 grams or more. So for a 5% preparation that's around 480 grams or roughly 1/2 kilogram. The bottom line is that you should not eat concentrated borax or boric acid products and if you plan on working around them frequently, you should use a mask to not inhale dust on a regular basis.
As for the 50 ppm Borates level used in pools, the EPA uses a Margin Of Exposure (MOE) of 100 to be conservative for inter-species differences and statistical risk from small sample sizes. An infant would have to drink 1 tablespoon of pool water every day for their lifetime to be at 1/100th the level where male dogs saw first symptoms. Since there is no dermal absorption, this is why no one is particularly worried about the use of borates in swimming pools. The main concern would be for pool service people who add it to many pools, but they just need to avoid ingesting it and if in windy areas they can use a mask to prevent inhalation of dust. I've added pure boric acid to my pool without any problems -- it's generally a reasonably fine powder, but not like baby powder or anything like that.
I need to correct my post. the 1 tablespoon per day for an infant is 1/100th the level of no observed adverse affect in dogs. The actual level for adverse effects was 3 times higher, but they didn't test in between so one uses the lower number as the "safe" level that is then factored by 100 to get allowed exposure. Also, daily exposure is not lifetime, but long-term so at least a month or more similar to the studies. Since the borates do not bio-accumulate, any longer exposure isn't proportionately worse (i.e. it's not statistical like cancer risk).
Borates are not mutagenic, carcinogenic nor do they create chromosomal damage. The only reason they are listed in the CMR is for the toxicity effects including that on reproduction. Again, one needs to use care in handling concentrated chemical, but that is true for most pesticides. Once diluted in the pool, it is generally safe unless one regularly drinks very large quantities of pool water. Some people play it safe with their dogs that use the pool as a water basin and either train their dogs to use a fresh water bowl or they avoid the use of borates.
One more update. The LD50 mg/kg toxicity levels that I quoted were for weight of Boron since that is how concentration is measured when one says 50 ppm for pools (i.e. it is 50 mg/L of Boron). For boric acid itself, the LD50 is 3,450 mg/kg for male rats so the fatal one-time dose for half the people (if affected similarly as rats) would be a little over 200 grams or about 7 ounces volume of boric acid. To put this into perspective, this toxicity level is roughly comparable to that of common table salt (sodium chloride) which has an LD50 for rats of around 3000 mg/kg.