CYA GONE....Hey ChemGeek!!!!

[kenlorz]

OK, Here's the deal.. pool has been great all summer, no major adjustment accept for one ph up ( was low after heavy rain)and one bag of salt. TC has been good holding 3.5-4.5 ppm with swg at 50%, filter running from 9-6 and the 2-330(am) every day. The last two weeks I had to bump up the swg..we seeemed to be using a lot more cl. I chalked it up to the extra heat and pool water being ~88deg or better daily. Also if I'm not in the pool the solar cover is on....always. Long story short we've had a very humid and rainy week. Today I rolled up the cover and about died! WhEW!!!! Pool stunk like dead fish and was a little cloudy with a very slight green tint...AHHHHHH . CL was at 0, ph 7.2 ak 120, salt 2850 and here's the kicker..my cya was 0. I'm new to IG with the swg, am I supposed to be checking/adding cya on a regular basis. It never dissapered like that in my old AG and I used to use unstablized tri-chlor pucks. Either way I've been at it all day, added 4.5 gal of 6% to get back on the chart, then added two bags of sodium shock ( using up left over stock from ag ), srubbed the walls, let it set for a bit then vacumed, then threw in my extra ctg while I cleaned the other one...and amidst all this using the stocking method to add cya. It allready looks and smells :? much better! So where did my cya go! I have read about it being gone over winter closing but to just dissaper in the middle of the season is wierd. I haven't added a whole lot of water either....twice I was about 1" lower than norm and threw in the hose, mother nature has done the rest for me this year. If I had to guess I would say we've used maybe a foot of water this year...out of almost 21k I really don't think that's alot...maybe I wrong. Anyway I'm getting back to normal and I'll post numbers tomorrow....in the meanwhile all comments welcome and thanks in advace for any adivce.
PS ....Yep..I inspected the cell and it looked good..pool is new this year...and YES I LOVE IT!!!!!!! :lol:

 

[The Mermaid Queen]

Can't help you with what happened, but it sounds like you are on the right track to get things straightened out!

 

[waste]

Ken, sorry that I'm not as knowledgable as chem_geek, but I'll take a stab at this. I recently (2 days ago) had a SWCG pool that had clumps of (what looked to me) mustard algae, I heard a description before I went out there and remembered a post from the night before (in which Waterbear said "system support" was sodium percarbonate and Richard had said that the sodium percarbonate was a 'non-chlorine' shock for hard to kill things like white and pink 'bioscum') I added the recommended dose and saw the 'crud' rise to the surface! [THANK YOU SEAN!!! FOR THIS FORUM!!!! - as I've said before, I come here to learn and this info was 'just in time', by about 13 hrs :-D ] I would have been unable to correct this problem, in time for the major birthday party they had pained, without reading the posts from this site !!!!

I think you may have one of those chlorine resistant strains of 'nasty' in your pool and the use of sodium percarbonate , or LOTS of bleach will kill the d*mned stuff over time..

As I said, I'm not as good as Richard or Evan on this stuff, but I think what I've suggested will work for you. HAPPY SWIMMING! -once the problem is solved.

Edit- it's my understanding that some of the 'bio-nasties' 'eat' cya as food, which could explain why the cya went 'bye-bye' -- sorry I forgot to mention that!

 

[focalboy]

I have the same question as kenlorz. It is evident to me now that my FC was being used up fighting some bio-critter over the last 7-10 days. My CYA was at 60 and today it is around 35 on my taylor test. We have had a great deal of rain the last week and my water level is a little high. So where is the CYA? I thought the only way to get rid of it was to replace water. Dilution would not change it that much, would it?

 

[waste]

focalboy, though I've only read about 'bionasties' eating chlorine over the winter, I've seen cya almost 'disapear' overnight. I'm speculating that the 'biofilm' eats enough chlorine and cya to allow some of the more persistent types of algae to take hold. I'll stop trying to give advice, other than what I've posted, untill we can hear from chem_geek and/ or Evan.

 

[kenlorz]

focalboy, being I live in the next state over (Pennsylvania), I got the same rain you did. Since I haven't tested my CYA since late spring, I have no idea how quickly mine dissapated. All I know is everything was fine until a week or so ago when we started getting inches of rain. Maybe we are fighting the same ''nasty'', eh?

 

[kenlorz]

Waste, what is sodium percarbonate? I know it's found in Oxyclean, other than that, don't know. Where did you get it and where did you find the recommended dosage? Thanks.

 

[mbar]

I read somewhere on the forum that sometimes ground water comes up through the hydro????something pipe (the one that lets some water in so the pool won't float out of the ground), and the bionasties come from the ground water that was in contact with soil.

 

[chem geek]

Though we know that certain soil bacteria will consume CYA and turn it into ammonia, such bacteria should not be alive in a pool with chlorine. That's why it made sense when this lowering of CYA occurred over the winter in pools that were "let go" and had zero chlorine levels.

Maybe some other types of organisms including some types of algae may be able to consume CYA (I'm speculating here). If they do and produce ammonia, it would take a LOT of chlorine to get rid of the ammonia. The CYA biodegradation pathway is shown here and you can see that CYA breaks down as follows (with biological enzymes that help the process):

CYA + 2H₂O --> Biruet + H⁺ + HCO₃^-
Biruet is essentially a cleaved CYA ring so now we have a chain instead of a ring.

Biruet + H₂O --> Allophanate + NH₃ + H⁺
So we get one ammonia at this stage (also, allophanate is negatively charged).

Allophanate + H⁺ + H₂O --> 2CO₂ + 2NH₃

So the overall net reaction is:

CYA + 3H₂O --> 3NH₃ + 3CO₂
Cyanuric Acid + Water --> Ammonia + Carbon Dioxide

So one molecule of Cyanuric Acid breaks down into 3 molecules of ammonia. It takes 1-1/2 molecules of chlorine to breakdown one molecule of ammonia so in ppm terms this means that for every 1 ppm CYA that is broken down into ammonia, it takes 2.5 ppm Free Chlorine (FC) to break down this ammonia (to nitrogen gas). So, a 10 ppm drop in CYA would take 25 ppm FC to get rid of the subsequent ammonia. That's a lot!

So while I don't have an explanation for the drop in CYA except speculation that some algae may break it down to ammonia, if this happens it would take a LOT of chlorine to get rid of the resulting ammonia. Also, if this is what happens, I would expect that the initial chlorine addition would show a very high Combined Chlorine (CC) level unless sunlight is helping to break it down quickly (so after a drop in CYA with algae present, then if you added some chlorine at night and saw a huge increase in CC, then this speculation of mine might be right).

Richard

 

[kenlorz]

Thanks for all the info.....richard you still amaze me! :-D I think we're going to be ok. Today's # are
TC 5.0
PH 7.6
AK 120
CYA 80....(added about 10lb yesterday)
Salt 2850
I don't have a cc test...I never did get one this year. I've been using the HTH 5-way from wally world. The good news is I let the pool run all night and I actually gained TC....it was about 3.5 at 11:00 aand a full five this moring with the swg back down to 40%. I know that I could still have a high cc...I'm going to hit the pool store when they open and get another full test done. The other thing that does encourge me is when my wife had it tested yesterday at the store my TC was ~1.5 with CC @ 0 about three hrs after adding a few gal of bleach and two bags of shock. I already vacumed and re-cleaned the filter today, I added some clarifiyer last night....I tend to frown on using it but, i think in this case it helped as there was a lot of dead alge on the bottom this morning. I Shocked it one last time and gave it a half dose of aglacide and I guess time will tell! I also found an interesting bit on the net.....and basically whenever your salt levels drop you should cya and check your CYA....LOL! For every 50 lbs of salt you lose you will also lose 1.5 lbs of cya! I did not know that. Have a good day all and I'll report back later.

 

[focalboy]

Kenlorz, thanks for letting me piggy back on your thread. We got more rain last night...comin your way.

Richard, thats exactly what I was thinking. Haha. Thanks for the science behind the problem.

I am going to go test my water now. I had my FC up to 5 last night and .6 CC. I maybe on the road to recovery.

Mark

 

[KurtV]

My guess is that the apparent drop in CYA was due to one or more or all three of these:

1. Testing error when the water was tested in the spring; you had less than you thought. This is possible given the subjectiveness of the CYA test
2. Water loss through splash-out, overflow, etc. Some of the drop is certainly attributable to this.
3. Testing error when the water was tested recently; you had more than you thought. This seems very likely given the quick rise in CYA you saw only a day after adding some. It usually takes at least several days for CYA to dissolve completely and show up on the test.

 

[chem geek]

Today I rolled up the cover and about died! WhEW!!!! Pool stunk like dead fish and was a little cloudy with a very slight green tint...AHHHHHH . CL was at 0, ph 7.2 ak 120, salt 2850 and here's the kicker..my cya was 0.

Though everything Kurt says as possible explanations may be a factor, perhaps this is just as simple as having the following sequence of events:

1) algae develops and overwhelms the SWG production of chlorine.
2) chlorine level drops to zero as algae develops and uses up the chlorine (i.e. some, but not all, algae gets killed).
3) bacteria then thrive at the zero chlorine level.
4) the bacteria consume the CYA converting it to ammonia.

The above scenario is not unlike what happens in the winter closing without continued chlorine addition or use of an algaecide. The "smell" was probably ammonia. The only thing that doesn't make a lot of sense is how the SWG got so readily overwhelmed with chlorine consumption -- I would have thought it would have still kept outputting at least some chlorine. Maybe for some reason the SWG shut down or maybe the weather plus cover being on had some sort of extra algae growth trigger -- this part is the mystery.

The part about "For every 50 lbs of salt you lose you will also lose 1.5 lbs of cya!" you found on the net just refers to the simple rule of dilution. In a 10,000 gallon pool, 50 pounds of salt is around 600 ppm while 1.5 pounds of CYA is around 18 ppm. So in a 3000 ppm salt pool, that's 90 ppm CYA so close to the 60-80 range normally recommended for SWG. Diluting with water that has no salt or CYA would reduce the salt and CYA by close to the 50 pound to 1.5 pound ratio quoted. Calcium Hardness and Total Alkalinity would also both drop as well with dilution unless these parameters are not low in the fresh water that is added.

Richard

 

[kenlorz]

I think you're right on the money Richard. Either way I just got back from the pool store and all looks pretty good...
TC 4.5
FC 4.5 wich means CC =0 8)
CYA 28....(I got about 75 this morning..I'll retest in 2 days, like I stated before I added a little less than 10lb)
PH 7.5
TA 120
CH 120
Salt 2850....Just added 40lb......should add about 250 ppm
TDS 3400...hence the very slighty cloudy water still
I'll let the filter run all night again and clean it this evening. In any case I beat it....whatever it was....and from now on....when in doubt-c.y.a. and check you CYA :lol:

 

[KurtV]

I think attributing the loss of CYA to bacteria is a stretch; I've never heard of this happening outside of a closed or abandoned pool where the zero chlorine condition was allowed to exist for a long time (like months). Then again, my experience is limited to the couple of pools I've owned and a few years on these forums; I'm ready to be wrong on this.

 

[focalboy]

Richards theory seems to be holding true for me as well. My salt is low in similar proportion to my CYA. My TA has dropped some as well. I have been running my Autopilot all day at level 3 60% as well as supplementing with 12% Chlorine. The water is clear, FC=5, CC=.4, but I have some white grit on the bottom of the pool. Could this be scaling or remnants of the bio-nasty I am fighting?

 

[dontcry]

since you've received rains for days, I'd say dilution play a big part of reducing your CYA. with a initial reading of 60 +/- 15, and if you received about 20% of rain water to fill your pool in about a week, CYA level could be drop to range 36~60 +/- 15.

 

[KurtV]

Richards theory seems to be holding true for me as well. My salt is low in similar proportion to my CYA. ...

The fact that your salt level dropped proportionally is strong evidence against the CYA-eating bacteria theory. Your dropping CYA is almost certainly the result of normal splashout and/or backwashing and/or overflow.

kenlorz, I see you've recently added at least 40 lbs. of salt; did you have to add more earlier in the summer?

 

[chem geek]

That's the nice part about saying two things in one post -- one of them is bound to be right! :-D

I, too, am surprised by how quickly the CYA went down. On the other hand, he did report that in the weeks before the one week the pool was covered without examination, the SWG had to be turned up more and more. I suspect that an alage bloom was developing so by the time this final week started, it was in full force and overwhelmed the SWG chlorine output (this is why one needs to shock with extra bleach or chlorinating liquid when the water is just dull or if the chlorine consumption goes way up rather quickly). The cover may have increased the water temperature having the algae grow faster as well.

If the chlorine level dropped to zero in the first days of that infamous week, then IF there were some bacteria that then dropped in to the pool (i.e. bacteria living outside the chlorinated water -- say on humid pool edges, etc.) then they could start to multiply. The generation (or doubling) rate for bacteria is from 15 minutes to an hour so let's just say it's 30 minutes. Then, one bacteria would turn into around 10^14 in a day, 10^28 in two days, 10^57 in four days. Of course, their growth was probably limited at some point by the nutrients available in the pool, but the point is that bacteria can grow VERY quickly.

I'm guessing that the degradation of CYA over the winter takes longer (i.e. months instead of a week) because of the much colder temperatures since all chemical processes slow down significantly (as do bacteria reproduction rates) at colder temperatures. But at the higher pool water temperature under the solar cover, things can happen pretty quickly.

Of course, this does appear to be a rare event, regardless of its cause. There are many, many pools that get to zero chlorine and have algae blooms and probably have bacterial growth as well, yet the CYA doesn't usually go down noticeably. So if this theory is correct, then something is different about this situation -- the type of bacteria, the conditions for growth, etc.

Richard