Pool Drained Twice Due To Cyanuric Acid

[OKC Goddess of the Sun]

Our pool has been drained twice now due to high cyanuric acid levels. According to my research thus far, it should take at least five years after a draining to build up enough of this acid for another draining. How could this have happened?

[LegsOnEarth]

What kind of Chlorine do you use? 5 years seems like a very optimistic estimate if you are using tabs to chlorinate it all year. It's even more unlikely if you are using granular dichlor.

For every 1ppm of Chlorine a Tab adds, it also increases the CYA by .6ppm

For every 1ppm of Chlorine granular Dichlor adds, it increases your CYA by .9ppm

Why did you have to drain though? How high was the CYA level? You could just as easily switch over to using Liquid Chlorine while you let the CYA drop naturally over time. I think you may have been sold a bill of goods...

[chem geek]

If typical daily Free Chlorine (FC) usage is 2 ppm (mostly from breakdown from sunlight if the pool is in the sun all day), then using Trichlor tabs would increase Cyanuric Acid (CYA) by 36 ppm per month so it doesn't take long to build up the CYA level if you don't have water dilution. In my own pool years ago I used Trichlor pucks and had a low 0.7 ppm FC per day chlorine usage because I had a mostly opaque electric safety cover. Even so, I went from 30 ppm CYA to over 150 ppm CYA in 7+4=11 "summer" months over 1-1/2 seasons and my pool then couldn't hold chlorine and got dull/cloudy from an impending algae bloom. I had an oversized cartridge filter so had no backwashing and it only needed to get cleaned once a year. I also used a pool cover pump and put the water to the sewer drain so got no water dilution from winter rains and our summers are dry.

I don't know where your research indicates it would take 5 years for the CYA to build up. If one has a short swim season, has summer and/or winter rains with overflow, has a sand filter backwashed weekly, and has a smaller pool, then I can see how the CYA may not build up. Also, in some pools that are "let go" over the winter, there can be a bacterial conversion of CYA into ammonia, nitrogen gas and/or nitrate so the CYA can drop, but this isn't reliable and if ammonia gets produced then the chlorine demand upon opening is huge.

Ever since that early disaster with my pool and subsequently finding The PoolForum I now just use 12.5% chlorinating liquid about twice a week and some Muriatic Acid as needed and it costs me around $15 per month for a 16,000 gallon pool. The pool is now used daily, but because it still has an opaque electric safety cover, the chlorine usage is still relatively low at somewhat under 1 ppm FC per day even though the pool is kept warm at 88ºF. I have no need for algaecides, phosphate removers, clarifiers, flocculants, enzymes or other products.

[OKC Goddess of the Sun]

Duke of Distribution: We are using tabs to chlorinate. We were forced to drain both times due to high levels of CYA. What those levels were - I don't know. I left it up to my pool service company to test the CYA, but apparently they were not doing that. I feel as though I've been duped.

Wizard of Water: Thank you for your information. We have a 26,000 gallon pool. I feel as though we've had good dilution. There was a time when I was adding fresh water to the pool on a weekly basis. In addition, the pool is backwashed weekly. Unfortunately, my research came from trolling the internet, which is what landed me on this website. I was not trying to project it as the end-all, be all. I came here for guidance.

In any event, I am looking for a new pool company this week. Something seems fishy on more than one level. Thanks for your help. If anyone has anything more to add, please do so!

[LegsOnEarth]

I would definately make sure that whoever you decide to go with in the future leaves a full report weekly of your pool's chemical readings. My service left a door tag each visit with that information for our customers piece of mind (even though the average home owner usually has no idea what the numbers mean, haha!). The point being that you should be able to show that information to any pool professional should you ever have any questions about the quality of your service.

Don't trust a company that isn't willing to be scrutinized. Good Luck!

[waterbear]

If you continue to use stabilized chlorine (trichlor and dichlor) you will continue to have problems with overstabilization (high CYA). Period, end of story! Switching to an unstabilized chlorine source will require either daily chlorine additions yourself (usually in the evening--it's really not a lot of work) or adding some type of automatic feed system designed for either sodium hypochorite (liquid chlorine or bleach) such as a peristaltic pump system or cal hypo (usually not readily available for residential pools at a reasonable price) or a SWCG (high initial cost but offset by the convenience factor in the long run).

The reason trichlor is popular is that it is the only form of chlorine that is suitable for use in an erosion feeder or floater because it is the only form of chlorine that is slow dissolving. Its downside the fact it is a chemical made from chlorine and CYA (a chlorinated isocyanurate) so once the chlorine it adds is used up the CYA stays behind. IF you live somewhere with a very short swim season (3 months) winterize the pool every year (which involves draining some water) and have a sand filter that you backwash weekly it is often possible to extend the period of time before you need to do a water replacement to lower the CYA. If you have an extended swim season , a cartridge filter or DE filter that is not backwashed freqently, and you do not winterize then using trichlor and dichlor are not your best choices for chlorination unless you don't mind the drain and refill dance!

Just adding water to the pool to make up for evaporation will not lower CYA. You have to drain water and replace it to lower CYA.

Also, please don't call me village idiot! My name is waterbear. Villiage idiot is my title much as your currently is Newbie. The others that answered you are LegsOnEarth and chem geek.

BTW, you might find this thread useful:

http://www.poolspaforum.com/forum/index.php?showtopic=37328&hl=&fromsearch=1

[chem geek]

In any event, I am looking for a new pool company this week. Something seems fishy on more than one level.

There is a lot of information that is either not disclosed or is just plain wrong in the pool/spa industry. Whether it's intentional deceit or ignorance is hard to tell, but either way it causes a lot of problems for pool owners and a lot more chemical sales and profits for pool stores, distributors and manufacturers. The following are chemical facts that are independent of concentration of product and of pool size, but are not normally disclosed:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.

For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.

For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

For every 10 ppm FC added by ANY source of chlorine, the salt level will increase by 8 ppm when the chlorine is used/consumed since it converts to chloride. Bleach and chlorinating liquid (and lithium hypochlorite) add an additional 8 ppm salt upon addition.

So continued use of stabilized chlorine (Trichlor or Dichlor) can often lead to a build-up of CYA. CYA reduces chlorine effectiveness unless you proportionally raise the FC level to keep the FC/CYA ratio constant. This chlorine/CYA relationship has been known definitively since at least 1974, but is not generally disclosed so specifically. To prevent algae growth in pool regardless of nutrient (e.g. phosphate, nitrate) level, the FC should be a minimum of 7.5% of the CYA level (saltwater chlorine generator pools can have a minimum FC of 5% of the CYA level). By following this rule, one can avoid the need for algaecides, phosphate removers, clarifiers, flocculants, enzymes and there is no need for any weekly or regular shocking.

[LegsOnEarth]

Just adding water to the pool to make up for evaporation will not lower CYA. You have to drain water and replace it to lower CYA.

Is that truly the case? I would love to see the science so I have it for future "I told you so's", but I have always been under the impression that CYA will drop over the winter months if I when I change over from Tabs to Bleach. I understand that some of that is ammonia convertion, and I have also been informed that CYA is a "Sticky" (VERY TECHNICAL TERM) chemical that will bond to you plaster and filters and everything, meaning that even after a full drain you will usually have a residual in your pool upon fresh filling.

So yeah, hit me with your best science.

[waterbear]

There is some degradation of CYA from chlorine over time but it is small and basically inconsequential. There is also loss from splashout and backwashing. My point is that when water evaporates it will concentrate whatever is dissolved in the water (such as the cyanurates). Adding water to make up for evaporation just brings things back to the initial levels.

Also, not all pools are closed for the winter (mine for example) and of those that are only a small percentage show degradation of CYA to ammonia. It requires aerobic conditions to occur and the introduction of the proper bacteria. When CYA levels are extremely high (a few hundred PPM or higher) it is entirely possible for cyanurates to precipitate out of solution and coat pool and plumbing surfaces just as any other precipitate can. It is not that CYA is sticky. It is more like a scale deposit made of stabilizer. As water changes are made and the CYA in the water is brought down this coating can redissolve and bring the level back up again necessitating more dilution. This effect is not really seen in pools that have not suffered from extremely high CYA levels.

[chem geek]

Imagine that you have 50 milligrams of Cyanuric Acid (CYA) in one liter of water, so that's 50 mg/L which is 50 parts-per-million (ppm). Now evaporate half of the water and remember that while water evaporates, CYA does not. So now you've still got 50 milligrams of CYA, but it's now in only 0.5 liters of water so 50/0.5 = 100 ppm. The concentration of CYA just doubled. Now refill back up to 1 liter by adding 0.5 liters of tap water which has no CYA in it. So now you are right back to the 50 milligrams of CYA in 1 liter of water that you started with. Evaporation with refill does not change the concentration of any pool chemical that does not evaporate and where there is no such chemical in the refill water.

Now compare this against a water drain and replace. So with the example I just used, drain half the water which removes BOTH water AND CYA. So now instead of 50 milligrams of CYA you have only half as much or 25 milligrams and you have half as much water or 0.5 liters so 25/0.5 = 50 ppm CYA. In this case, the concentration of CYA stayed the same, but now refill back up to 1 liter by adding 0.5 liters of tap water which has no CYA in it. So now you have 25 milligrams of CYA in 1 liter of water or 25 ppm CYA which is half the CYA level you started with. A drain/refill will dilute the concentrations of any chemicals in the pool water by the amount of dilution so long as such chemicals are not found in the fill water.

As for CYA staying in pools that are completely drained, there does seem to be some remnant of CYA in these cases, but it's not a lot. As to whether it's due to the chemical "sticking" to pool surfaces, that appears to be one of those speculative guesses that has no scientific literature to back it up. It's not impossible for an organic compound to have some affinity to PVC which is organic, but it seems less likely to have such affinity to calcium silicate and calcium carbonate pool surfaces. At any rate, though that completely drain and refill their pools usually report that the CYA test shows way less than the 20 ppm CYA limit of the test, but some see a slight cloudiness in the test indicating that something may still be there. I would say the jury is out on this one.

One piece of baloney you may hear is that CYA is heavier than water so stays near the bottom so that one should drain from the bottom. This simply isn't true for any substances that dissolve fully in water and CYA is one of those substances since it is not saturating pool water. Fully dissolved substances do not separate and with pool depths they do not stratify (by any reasonably measured amount). That's part of the definition for them being dissolved as opposed to simply mixed or even being a suspension.

[LegsOnEarth]

Thanks fellas,

I get a lot of flak in these parts for telling folks to use as little granular and tablet chlorine as possible, so I'm always happy to stock up on more ammunition for my arguments. I've also read those studies from the 70's that Chem Geek posted here and I use those as my primary basis for arguments.

Unfortunately, most pool guys are pretty stuck in their ways, so I can only educate so much before it's back to tabs and dichlor.

[waterbear]

Nothing wrong with using dichlor, cal hypo, or trichlor if you use the PROPERLY. Trichlor is wonderful to use when starting up new plaser (because of it's low pH) and I use dichlor in my own salt pool whenever I need to bring the CYA level back because it dissovles much faster than CYA and I only need to raise the CYA about 10-20 ppm. Cal hypo can be used effectively if you know the way to do so!