[macgd016]

My pool is in southern Spain and I found earlier in the year that although the CYA was very high, 400ppm. I recognize that I should drain the pool and start again but there is a major water shortage in Spain and re-filling pools is not permitted. The house is let out over the summer and we have been managing to maintain the pool very successfully since June by keeping the FC at about 10ppm and using Algaecide, fortunately for us we are almost phosphate and nitrate free one benefit of living in the mountains and using what is essentially mountain spring water.

Unfortunately we have just had one family stay at the house who, despite being advised to the contrary, have used lashings of suncream and splashed so much that the skimmers were sucking air after only 2 days!! The end result is that we have algae. We first found this yesterday and have hit it twice with double the normal dose of GR90, which is a 90% available Trichlor granule, and having the pump on 24h, adding more algaecide and crystal clear to help with filtration. My calculations suggest that the shock treatment will raise the FC by 16ppm and although the FC is falling back to 3ppm it is having an effect, the water is clearing and you can see the bottom and there is quite a bit of dead algae on the bottom which we have hoovered out, but the water is still green.

As we have guests staying at the house I really want to get the water good and clean as quickly as possible whilst still letting them swim. Using the pool calculator I have calculated that with a CYA level of 400ppm I need raise the FC to 75ppm to shock it and this will need about 1 gal of 10% bleach.

From what I have read this is still a perfectly safe level of chlorine to swim in but I just wanted to check before going ahead. Any other suggestions as to how to proceed would also be welcome.

[macgd016]

My pool is in southern Spain and I found earlier in the year that although the CYA was very high, 400ppm. I recognize that I should drain the pool and start again but there is a major water shortage in Spain and re-filling pools is not permitted. The house is let out over the summer and we have been managing to maintain the pool very successfully since June by keeping the FC at about 10ppm and using Algaecide, fortunately for us we are almost phosphate and nitrate free one benefit of living in the mountains and using what is essentially mountain spring water.

Unfortunately we have just had one family stay at the house who, despite being advised to the contrary, have used lashings of suncream and splashed so much that the skimmers were sucking air after only 2 days!! The end result is that we have algae. We first found this yesterday and have hit it twice with double the normal dose of GR90, which is a 90% available Trichlor granule, and having the pump on 24h, adding more algaecide and crystal clear to help with filtration. My calculations suggest that the shock treatment will raise the FC by 16ppm and although the FC is falling back to 3ppm it is having an effect, the water is clearing and you can see the bottom and there is quite a bit of dead algae on the bottom which we have hoovered out, but the water is still green.

As we have guests staying at the house I really want to get the water good and clean as quickly as possible whilst still letting them swim. Using the pool calculator I have calculated that with a CYA level of 400ppm I need raise the FC to 75ppm to shock it and this will need about 1 gal of 10% bleach.

From what I have read this is still a perfectly safe level of chlorine to swim in but I just wanted to check before going ahead. Any other suggestions as to how to proceed would also be welcome.

Anybody!

[quantumchromodynamics]

If one gallon of 10% liquid chlorine will raise your free chlorine to 75 ppm, then your pool must only be about 1300 gallons, is that correct? I recommend against raising your chlorine that high.

You have to stop using trichlor and dichlor; they are adding more cyanuric acid to your pool. You really need to dilute the water to lower the cyanuric acid, 400 is way too high. Besides the effect that it has on the chlorine, there is also some toxicity concern, although I am not sure what the actual risk is. It is my opinion that the pool should not be used by anyone until you get your cyanuric acid to an acceptable level.

One thing you can do is switch to bromine by adding 0.25 to 0.50 pounds of sodium bromide. Bromine is not affected by cyanuric acid. Use regular, unscented Bleach or liquid chlorine to convert the bromide to hypobromous acid. Maintain a bromine level of about 2 ppm to 8 ppm. Get the Taylor K-2106 test kit.

You will need to test the bromine level every day and add liquid chlorine or regular unscented bleach to keep your bromine levels consistent. Use 8 to 16 ounces of 6.00 % bleach and then retest after 1 hour.

Who tested for cyanuric acid and how did they test?
What are your other chemical readings? pH, Alkalinity, Calcium Hardness, TDS?
What kind of pool is this? Concrete, vinyl liner, fiberglass?

[chem geek]

The high CYA level makes the chlorine less effective (at the same FC level; that is, unless you proportionately increase it to keep the FC/CYA level constant). This not only affects the rate of disinfection and algae growth prevention, but also the rate of oxidation of bather waste, suntan lotion, etc. As was noted in the previous post, you could turn your pool into a bromine pool to work around the CYA issue, but that will be expensive. Also, if your pool is really as small as implied by your calculations for the amount of chlorine needed, then I find it hard to believe that this amount of water will be that expensive. For the suntan lotion and other contaminants, you can also try scum balls, slime bag and skimmer socks as well as enzyme products.

With Trichlor, for every 10 ppm Free Chlorine (FC), it also increases Cyanuric Acid (CYA) by 6 ppm. So for the future you want to use chlorinating liquid or bleach to avoid the buildup of CYA.

[quantumchromodynamics]

____________________________________________
"Also, if your pool is really as small as implied by your calculations for the amount of chlorine needed, then I find it hard to believe that this amount of water will be that expensive." - Richard
_____________________________________________

The OP notes that refilling a pool is not permitted where they live. Perhaps they have not considered options such as having water trucked in.
__________________________________________

"As was noted in the previous post, you could turn your pool into a bromine pool to work around the CYA issue, but that will be expensive." - Richard.
___________________________________________

I don't think that it would be that expensive. A small amount of sodium bromide to convert and then bleach or liquid chlorine every day.

If their pool is only 1300 gallons then it would not take that much. I think that your calculations regarding chlorine or bromine loss to sunlight with no cyanuric acid protection overestimate the loss rate. I think that your calculations are for direct intense sun exposure. There are many times that pools do not get such intense exposure. Night, of course; cloudy days; shade from trees, fences and such etc.

During the morning and afternoon, the light is oblique. And, the loss rates that you calculate do not match my experience. A pool chlorinated or brominated in the morning will usually still have chlorine or bromine at night.

In this case, I think that 8 to 16 ounces of bleach on a daily or twice daily schedule would be sufficient. The homeowner could have the guests test the bromine level and add bleach as needed. To make it easier on the guests, the homeowner could just have them add a predetermined amount at the end of each day.

A solar cover could also be used to reduce losses due to sunlight.

[chem geek]

Yes, given the presumed small pool size, bromine shouldn't be that expensive and I don't really have good breakdown rates since there aren't very many bromine pool users on the forums.

[macgd016]

Thank you both for your replies. For the present I am stuck with a high CYA, this is not a 'cost' issue but a legal and social one. Up until last winter Southern Spain had had no appreciable rain for 4 years and reservoirs were at critically low levels. There was a slight recovery last winter but it is still illegal to fill pools and water supplies to houses are regularly (daily) cut for several hours during the summer. Although our pool is indeed small it still contains about the volume of water that would be used by a small family in 4 months so it is for this reason that I a) do not wish, and am not permitted, to refill it.

It is my intention to switch to an automated liquid chlorine system this winter which will stop any further increase in CYA and will enable it to be reduced over time through natural dilution. So for the meantime, as I tried to explain in my initial post, I am stuck with a high CYA level, I have no desire to switch to Bromine as I have no experience of it and more importantly there is little or no experience of it locally so I need to manage my pool as it is.

We have been managing to successfully keep the pool under control but some unexpectedly high usage last week caught us out and we now need to rectify the situation. From the excellent information I have gleened on this forum I now have an understanding of the relationship between CYA and FC and using the Pool Calculator can see that in order to shock the pool I need to raise the FC to 75ppm. I also believe that as 75ppm FC with 400ppm CYA is equivalent to 16ppm FC with 50ppm CYA it should be perfectly safe to swim in but I just wanted to check and to see whether there was any other advise out there.

For info the pool is 24x12, 1,300 US gals and all other readings are well in spec.

[quantumchromodynamics]

If someone were to use bromine tabs, that does get expensive for larger volumes of water. Bromine tabs can cost significantly more than chlorine tabs. Types of bromine tabs available.

BCDMH (1-bromo-3-chloro-5,5-dimethylhydantoin), also called organic bromine. Sold in tablet or granular form, it has a pH of 4.5–4.8 in a 0.1 percent solution and an equivalent available chlorine content of 58 percent

BCDMH + DCDMH + DCEMH (1-bromo-3-chloro-5,5-dimethylhydantoin + 1,3-dichloro-5,5-dimethylhydantoin + 1,3-dichloro-5-ethyl-5-methylhydantoin), sometimes referred to as Dantobrom S. In the spa market, this is retailed in both tablet and briquette form. The compound has a pH of 3.6 in a 1 percent slurry and an equivalent available chlorine content of 62 percent

DBDMH (1,3-dibromo-5,5-dimethylhydantoin). DBDMH disinfectants have a nearly neutral pH of about 6.6.

However, no one should use either chlorine or bromine tabs as their primary source of chlorine or bromine. Trichlor or bromine tabs should be used very carefully to avoid problems such as low pH and alkalinity and buildup of cyanuric acid and dimethylhydantoin (DMH). I would recommend the tabs not make up more than 20 percent of chlorine or bromine demand.

The lowest cost method of using bromine is to add 200 grams (7 ounces) of sodium bromide per 5,000 Liters (1,321 gallons) of water to establish a 30-ppm bromide reserve and then add liquid chlorine as needed to provide the necessary bromine. You can also use bromine tabs in a feeder to provide a continuous supply of bromine for convenience.

Reference:
http://www.taylortec...SP?ContentID=73

[quantumchromodynamics]

For info the pool is 24x12, 1,300 US gals and all other readings are well in spec.

24 feet by 12 feet? That would be a lot more than 1,300 gallons. 12 feet by 24 feet by 4 feet deep would be 8,640 gallons.

Bromine really isn't that hard. Just add 8 ounces of sodium bromide, then just use liquid chlorine, and treat your pool as if it was chlorine.

12 feet by 24 feet by 4.5 feet deep would be 1300 cubic feet. Is that what you mean?

[macgd016]

For info the pool is 24x12, 1,300 US gals and all other readings are well in spec.

24 feet by 12 feet? That would be a lot more than 1,300 gallons. 12 feet by 24 feet by 4 feet deep would be 8,640 gallons.

Bromine really isn't that hard. Just add 8 ounces of sodium bromide, then just use liquid chlorine, and treat your pool as if it was chlorine.

12 feet by 24 feet by 4.5 feet deep would be 1300 cubic feet. Is that what you mean?

My mistake, I work in metric and the pool is 3.6m X 7.5m 1.8m giving 48,000 litres or roughly 13,000 US gallons.

[quantumchromodynamics]

I'm not so sure that the 400-ppm reading for the cyanuric acid is reliable. Make up a sample of water using 1 part pool water to 9 parts tap water and have the sample tested. Multiply the result by 10.

If your cyanuric acid really is that high, I would not consider the pool safe to use. I recommend that you close the pool until you can figure out a way to dilute the water and get the cyanuric acid to an acceptable level.

[quantumchromodynamics]

There is one way to lower cyanuric acid without draining and refilling.

First, you deoxygenize and dechlorinate the water, and then you add cyanuric acid reducing anaerobic bacteria. The bacteria will convert the cyanuric acid into carbon dioxide and ammonia. Then you oxidize the bacteria and ammonia with chlorine, hydrogen peroxide, sodium percarbonate or sodium perborate.

You will have to research this yourself, as it is not a standard procedure, especially finding the right bacteria. Actually, I don't think that anyone has ever intentionally done it on a pool, and I don't know how safe it is.

This might be a good business opportunity for someone who inadvertently gets this bacterium. You could get some sort of holding tank to culture the bacteria and sell a gallon of the bacteria water for whatever you think it is worth.

[quantumchromodynamics]

Two more things that you should consider.

First, if this is a concrete pool, you need to maintain a non-negative Saturation Index. When calculating the SI, you need to subtract 1/3 of the cyanuric acid level from the total alkalinity to get the carbonate alkalinity. As your level is 400, then you have to subtract 133 ppm from your total alkalinity reading.

Second, if you are going to use an algaecide, you should only use PolyQuat 60. You should avoid copper due to the potential for staining. With such a high cyanuric acid, if you did use copper, you would be at risk for copper cyanurate stains, which are purple.

[billp]

If your cyanuric acid really is that high (400 ppm), I would not consider the pool safe to use....
First, you deoxygenize and dechlorinate the water, and then you add cyanuric acid reducing anaerobic bacteria. The bacteria will convert the cyanuric acid into carbon dioxide and ammonia...
You will have to research this yourself, as it is not a standard procedure, especially finding the right bacteria. Actually, I don't think that anyone has ever intentionally done it on a pool, and I don't know how safe it is.

On what basis do you NOT consider the pool safe? A person would have to drink several hundred gallons of this water to get enough CYA to be toxic. There are many pools & spas with excessive CYA levels due to trichlor and (especially) Dichlor use, the highest I have measured was a hotel pool with 800 ppm. I have NEVER heard of any ill effects to swimmers or subsequent lawsuits. Please note, I am addressing SAFETY not good water chemistry. (I do NOT advocate high CYA levels.)
Somehow it seems your recommendation for using a non-standard procedure with anaerobic bacteria would be FAR more hazardous than 400 ppm CYA. And you are recommending a procedure you admit "I don't know how safe it is." What if he finds the WRONG bacteria? Bet it is a lot more hazardous than a little bit of well-contained diluted acid...

[chem geek]

The EPA sets a (ridiculously low) FC limit of 4 ppm though several state codes allow up to 10 ppm. The EPA limit is based on drinking water standards where you drink 6-8 quarts per day every day. They say that they apply this standard to pools because of unknown skin absorption rates for chlorine and that no field studies (which cost millions of dollars to do) have been done to prove safety above that limit for pools. In practice, with CYA in the water, most of the chlorine is bound to CYA and CYA has been shown to not absorb through the skin very much at all (see here).

I think the main issue with safety would be if the FC level were "standard" at 1-3 ppm FC with the CYA very high. In that case, the chlorine kill rates would be very low. Certainly, algae could grow, but heartier bacteria could as well. As to how unsafe this is, that's a matter of debate.

Even though I have faith and confidence in the chemistry of FC/CYA, I would be at least cautious and avoid swimming while the water is being shocked at 75 ppm FC with 400 ppm CYA. If the chlorinated cyanurates (that is, chlorine bound to CYA) had some even small sanitizing or oxidizing effect, the 75 ppm could become significant. If after shocking the FC dropped to a managed level of 20-30 ppm, that still seems high but would be seemingly more reasonable. In this kind of situation, if the water cannot be diluted to lower the CYA, it might be better to use an algicide such as PolyQuat 60 and go with lower 10 ppm FC chlorine levels, assuming this combination is enough to prevent algae growth.

[quantumchromodynamics]

First of all, I never recommended the anaerobic bacteria procedure. I never said that I thought it was a good idea. I never said that I thought they should try it. I was merely providing information.

I clearly said that it wasn't a standard procedure, and that I didn't know if it would even be safe. I said that the person would have to research this themselves. I feel like I gave sufficient disclaimer.

Someone has to be the first one to try something. Perhaps this person would want to try it, that's up to them.

Of course, the pool would have to be closed to swimmers if the person were going to try this.

I consider 400 to be unsafe, that's my opinion. 400 is unacceptable. 400 is ridiculous. There has to be a limit where you say close the pool.

This person is renting out the house with the pool. I doubt that the renters are aware of the chemistry of the pool that they are swimming in.

It would be one thing if the person were the only person swimming in the pool and they were making an informed choice, but as this is a semi commercial operation, the maintenance has to be held to a higher standard.

[quantumchromodynamics]

A person would have to drink several hundred gallons of this water to get enough CYA to be toxic.

Several (1). Adjective few: a small number, though more than two or three.

Four hundred gallons of water at 400 ppm contain about 1.33 pounds of cyanuric acid. Are you saying that anything below that is not toxic? Are you willing to eat 1.25 pounds of cyanuric acid to prove your point?

If you do decide to prove your point, please give someone your login information so they can post the results if you die.

[quantumchromodynamics]

At 400 ppm of cyanuric acid, thepoolcalculator gives a mustard algae shock level recommendation of 204 ppm.

Using the Cyanuric acid/Chlorine chart and extrapolating suggests a mustard algae shock of 156.

[chem geek]

I agree that 400 ppm CYA is pretty ridiculous and regardless of whether high FC levels would work reliably or be safe, it's clearly impractical. Extrapolating the FC/CYA relationship to levels where the absolute FC could become a more significant factor is unwise. Also, adding that much chlorine will have a significant effect on pH such that even lowering the pH first would not be enough to prevent the pH from rising a lot (at least until the FC dropped back down which would lower the pH again).

As for toxicity of CYA itself, see this link which has a No Observed Adverse Effect Limit (NOAEL) in rats of 150 mg/kg/day which for a 50 kg (110 pound) person (if similar to rats) would be 7500 mg which would take about 19 liters (about 5 gallons) at 400 ppm CYA. Acute oral toxicity (the lethal dose where half would die) for rats is 7700 mg/kg so for that same person would be 385,000 mg or 254 gallons. I don't think that the issue is one of CYA toxicity.

A completely different approach would be to simply use a sodium bromide product to effectively turn the pool into a bromine pool, at least until one gets rid of most of the excessive CYA. Bromine doesn't combine with CYA so even 1-2 ppm bromine would be a reasonable sanitizer and would kill algae. If one didn't overdose with the sodium bromide, one could eventually convert the pool back to chlorine in the future, though that could take weeks. The more I think about it, the more I think this would be more reasonable in this situation if the person truly cannot dilute the water to get the CYA lower. The main downside is the extra cost for bromine, but it should be less than the extraordinarily high FC levels one would otherwise need.

[quantumchromodynamics]

Here is another Idea.

Is there any source of clean water near where you live? Anything like a lake or river that you could get fresh water from? As long as the water is fairly clean, and not polluted, you should be able to fill your pool with it. I'm not sure about ocean water due to the high salt content, but that might be a possibility as well.

[chem geek]

Fresh water from streams, etc., OK. Salt water from the ocean, no way -- that's like 30,000-35,000 ppm salt. If it rains during the winter, then rain overflow would work and it's what I do in my own pool to refresh the water.

[quantumchromodynamics]

Richard, if the pool is not susceptible to corrosion, then what are the primary reasons that the high salt content would rule out using ocean water?

I don't think that there would be any health concerns, because people swim in the ocean. Obviously, if they drank any significant amount, then there could be adverse effects. Thanks for any information you can provide.

[billp]

A person would have to drink several hundred gallons of this water to get enough CYA to be toxic.

Several (1). Adjective few: a small number, though more than two or three.
Four hundred gallons of water at 400 ppm contain about 1.33 pounds of cyanuric acid. Are you saying that anything below that is not toxic? Are you willing to eat 1.25 pounds of cyanuric acid to prove your point?
If you do decide to prove your point, please give someone your login information so they can post the results if you die.

Very funny! Eating CYA would not prove my point. Too bad you missed my point. You said you considered 400 ppm CYA unsafe. I looked at the toxicity of CYA and found a person would die from a toxic overdose of dihydrogen monoxide LONG before dying from a toxic overdose of CYA in pool water. As you pointed out elsewhere, many pools have a high level of dihydrogen monoxide. Simple point.
While you may have other reasons for considering it unsafe it is simply your own opinion since there is (unfortunately) inadequate science upon which to base an opinion. And as I mentioned, in real life we don't see any safety problems related to high CYA. One can find plenty of safety problems related to inadequate chlorination/sanitation. The highly publicized cases of pool related illness are always due to inadequate (usually zero) chlorine, not high CYA levels. That's all.

[quantumchromodynamics]

One can find plenty of safety problems related to inadequate chlorination/sanitation. The highly publicized cases of pool related illness are always due to inadequate (usually zero) chlorine, not high CYA levels. That's all.

Very high cyanuric acid levels slow down the reaction rate of chlorine to a rate too slow to provide adequate chlorination/sanitation unless the chlorine levels are raised to dangerously high levels.

I challenge you to provide one authoritative source that says that a cyanuric acid level of 400 is acceptable. That's all, just one.

[chem geek]

Richard, if the pool is not susceptible to corrosion, then what are the primary reasons that the high salt content would rule out using ocean water?

I don't think that there would be any health concerns, because people swim in the ocean. Obviously, if they drank any significant amount, then there could be adverse effects. Thanks for any information you can provide.

Most pools are not designed to operate in such high salt conditions and yes, corrosion would be an issue, but so would irritation (stinging) of the eyes. People may swim in the ocean, but the salinity of the eyes is around 9000 ppm. There are concerns even at saltwater chlorine generator (SWG) levels which are 3000 ppm or so (see this blog for extreme examples) though generally the more serious corrosion rates happen above 5000 ppm or when there is no CYA in the water as with some indoor SWG systems. It's the combination of a strong oxidizer with higher conductivity that accelerates metal corrosion including high chloride levels with stainless steel (see this EPA PDF file).

[chem geek]

I would characterize a CYA of 400 ppm as unadvisable and with typical FC levels it is slow to kill pathogens. The easy-to-kill bacteria typically have a CT (chlorine concentration in ppm times time in minutes) value of around 0.08 for a 2-log (99%) kill. This translates roughly into a 50% CT of 0.01 so with a 15 minute generation time (being conservative; it's generally 15-60 minutes depending on conditions) this implies a required chlorine level of 0.00067 ppm. 2 ppm FC with 400 ppm CYA would have an effective chlorine level of around 0.005 ppm with no CYA.

So easy-to-kill bacteria that weren't in biofilms would still be killed faster than they could reproduce, but harder-to-kill pathogens (see this link) wouldn't and person-to-person transmission would not be inhibited very much at all and, of course, algae could grow since that generally requires even more chlorine to prevent its growth. So "safe" is a relative term. It's certainly less safe than more normal levels of chlorine with an FC/CYA ratio closer to 5-10% (compared to 1%), but it's more safe than not having any chlorine at all. Even with no chlorine, it's not like people immediately get ill if they enter the water; it's just unwise and in some infrequent cases it can be quite dangerous and even deadly (see this link, for example, as well as this link demonstrating that it is the hypochlorous acid and not the chlorine combined with CYA that does the killing).

Basically, having a pool with a CYA of 400 ppm is essentially having a pool with about 1/6th the amount of disinfection and oxidation capability as the more normal CYA of 50 ppm, all else equal.