Notes From Bob Lowry: The CYA Debate Continues

Swimming Pool

As many of you have noticed, the industry debate over the proper level of CYA has gained more intensity in recent years. Some may remember AQUA’s industry forum on the topic at the PSP Expo in New Orleans last year, which featured a lively discussion about recommended CYA levels and how pool pros should manage them.

Just to recap, FIFRA (the Federal Insecticide, Fungicide and Rodenticide Act is a U.S. federal law that sets up the basic U.S. system of regulation for sanitizers) says that the CYA-to-free chlorine level should be 20:1, and free chlorine should be 4.0 ppm max.

We know that 20:1 is 5%, so if free chlorine is held to a maximum of 4.0 ppm, CYA should be allowed up to a maximum of 80 ppm.

Keeping that 20:1 (5%) ratio, then, exceeding 4.0 ppm free chlorine would mean a corresponding CYA of more than 80 ppm. Or exceeding more than 80 ppm CYA would require a corresponding free chlorine of more than 4.0 ppm.

My own view is that the free chlorine level needs to be 7.5% of the CYA level unless borate at 50 ppm is being used in which case, the level needs to be 5% of CYA. On The Trouble Free Pools website, Ben Powell, Richard Falk and I have been urging tens of thousands of residential pool owners and residential service technicians to follow these guidelines since 2007.

Elsewhere, at this moment, the Model Aquatic Health Code (MAHC) has opened its position on CYA for revision, pending committee decision and voting. Concerned industry members can join the Council for the Model Aquatic Health Code (CMAHC) on its website, and vote for changes to the Code’s recommended CYA levels. Voting opened November 13.

Removing CYA Using Alum

In the midst of this debate, a topic that has drawn some attention in the last year is a method put forward by Rudy Stankowitz to remove CYA from pool water using alum (aluminum sulfate). If effective, this would be a better way to lower CYA levels than draining. This method should be given more research and study.

There are some questions and observations I have about using alum (aluminum sulfate) for CYA reduction or removal. I am not saying it does not work. I am offering some alternative conclusions and explanations. More evidence is needed.

No Scientific Literature

There is no evidence in the scientific literature anywhere that states alum (aluminum sulfate) can be used for lowering or removing CYA. This does not mean that it cannot be used for CYA reduction or that it does not work for that purpose. It only means that no one has documented or studied alum for CYA removal and published their work.

Alum Chemistry and Use

Alum is used in drinking water treatment, waste-water treatment, swimming pools and other industries. In water treatment, it causes suspended impurities to coagulate into larger particles and then settle to the bottom of the vessel (or be filtered out) more easily. This process is called coagulation or flocculation. When dissolved in a large amount of neutral or slightly acidic water, aluminum sulfate produces a gelatinous precipitate of aluminum hydroxide - Al(OH)3. The precipitate is called floc. The floc forms better when the pH is from 6.5 to 7.0. The gelatinous floc attracts and holds on to suspended particles in the water and settles to the bottom where it can be vacuumed or be drawn into the main drain.

Alum is used to coagulate suspended, negatively charged particles to make them larger and more conducive to filtration or sedimentation. The keywords here are suspended negatively charged particles.

In pool water, CYA is dissolved and not suspended. At typical pool water pH, CYA exists predominantly as the mono-an ion (H2C3N3O3)–. It can exist as five other species but about 94% is the mono-anion.

Alum-CYA Removal Method

The Alum-CYA Removal method calls for lowering pH to 6.8 to 7.0, adding alum at 8.3 lbs. per 10,000 gallons of pool water, mixing until the floc forms and settles to the bottom, and vacuuming to waste about 12 to 14 hours later.

This dose is about double the recommended dose of alum as a coagulant for mildly cloudy pool water. Adding alum to a pool that is not cloudy or turbid means that the alum can remain in the water for some time with no suspended particles to remove and a double dose has been added.

CYA Testing

The CYA test is turbidimetric (or cloudiness). The turbidity is due to the formation of an insoluble melamine-cyanurate precipitate when the reagent melamine is added to pool water containing CYA. One usually reads a black spot through the turbidity or even in some electronic equipment, a beam of light at a special wavelength is passed through a sample cell to determine the concentration of CYA.

Alum May Be Affecting the Test

Due to the high dose of alum to the pool water, low or no turbidity in the water, and a relatively short time until CYA may be tested (12 hours later), there may be some active alum in the pool water. Alum can remain active in the water for about 48 hours or longer if there is low turbidity or nothing for it to remove. When alum is present in the pool water along with CYA, the alum will coagulate the melamine-cyanurate precipitate reducing the turbidity just like it does in a cloudy pool. Reducing the turbidity in the sample will appear as an “apparent” reduced amount of CYA present. This is further evidenced by reports that alum has reduced CYA by a percentage instead of a ppm reduction. I see people writing saying that they lowered CYA by some percent. Usually, this is about 50%. They do not say that alum was reduced by a ppm. If alum was truly working as a removal method, then we would expect a reduction of some ppm per some dose of alum. Instead, we are hearing about reducing CYA by some percent.

Anecdotal Reports Say CYA Lowered Then Increased

Then we hear about pools that have “lowered” CYA by this method and sometime later the CYA has gone back up. They conclude that CYA was absorbed in the plaster, plumbing, filter or other equipment and now it is redissolving or releasing back into the pool water. Another explanation might be that there was alum in the sample when the CYA test was performed only 12 hours after adding a double dose to water that was not cloudy. The alum clarified the sample as the melamine-CYA turbidity was produced and gave a lower reading. Weeks later when all the alum in the pool water is gone, a CYA test now shows a higher CYA concentration even though no more CYA was added. The alternative explanation is that now that there is no more alum in the pool water, you now are getting an accurate CYA test result. This indicates that the alum may have clarified the initial CYA test giving a false reading.

Just an Alternative Explanation 

My logic, science-based conclusions are exactly that until proven or disproved. I cannot cite any direct articles or evidence. It is a possible explanation for the apparent reduction in CYA due to an alum dose. It is the reason that I am skeptical. Perhaps more testing and even revisiting some pools with success might show an increase in CYA after a few weeks. I have plenty of reports that say that alum removes CYA and plenty of reports that say that CYA goes back up a week or two later. I want to prove that this works before we all start recommending it only to find out that it doesn’t.

Is CYA Absorbed or Embedded into the Plaster?

The idea that CYA gets embedded or absorbed into the plaster is another phenomenon that needs to be investigated. We hear all the time that a pool has high CYA may be in the 300-500 ppm range. It is drained completely and a week after refilling the CYA is back up to 50-100 ppm with no CYA having been added. There was even a study and paper done on this recently concluding that this does not happen and there is no way CYA can absorb into the plaster. Well, there are lots of service techs who would disagree with that. On one Facebook group this week, I had five people tell me that they drained a pool due to high CYA and two weeks later they had 30 to 100 ppm CYA. So if CYA is not absorbing or embedding into the plaster, where is the CYA coming from? The filter? The pipes? False test due to alum coagulating the turbidity? We need some answers.

Now is the time for manufacturers to step forward with research or studies to find out what CYA is doing to plaster, equipment, fittings and water chemistry.


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