High chlorine levels affecting...pH and other results?

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DanaSC

Well-known member
May 16, 2012
150
Lexington, SC
I'm aware of high chlorine affecting pH levels, but I'm wondering if it also affects CYA, TA and CH. We thought we saw black algae in the pool last night and once I realized we didn't have any chlorine (I know, I know) in the pool, I quickly added bleach so the brushing we did wasn't for nothing. Then I continued with my testing, and started questioning the results of my testing when I got basically a reading of no CYA in our pool, which I found odd. Typically we use pucks, which I'm well aware add CYA to the water, and we didn't drain our pool much for the winter, so I'm not sure why it's showing no CYA.

What other readings does high chlorine affect, if anything?

I also suspect that it *might* be possible that we don't actually have black algae, but rather if my CH is low (if the test result is accurate even with higher chlorine levels), that instead maybe calcium is leaching from our plaster (that's possible, right?). I feel like that's more likely than the black algae, but I'm not really sure, but my plan (if my test results are accurate) is to get my CH, TA and CYA back to "normal" and then start the SLAM process.

Thoughts?
 
It might be ammonia. I would raise the FC to 10 and test 10 minutes later. If you've lost 50% or more of your FC then you likely have ammonia. Don't raise CYA until you are sure you don't have it.

But to answer your question pH is the only test that is not accurate at high FC (within reason)
 
Stealing this from Texas Splash:
Okay, then here's what you need to do:
1 - Lower pH with acid to about 7.2. Check about 20 min later with pump mixing to confirm change is good
2 - Before adding any stabilizer, do the 10-min drill ... perfect if it's cloudy at your place like mine today - we're checking for ammonia
2a - Raise FC to 10; check every 10 minutes. If it drops below 5, raise it to 10 right away again and keep doing this every 10 minutes
2b - Once your FC holds over 5 or close to 10 after 10 minutes, add granular stabilizer for a CYA target of 30 and increase FC to "12"
Now you're SLAMming! Check FC consistently to ensure is stays at 12. Let me know if you have any questions.
Click to expand...
 
Ammonia is from CYA being converted by bacteria. So, if you had CYA at the end of the season, and now you don't have any CYA, your CYA is now ammonia. I have had this happen to me several times.

Your first step is to illuminate the ammonia as mentioned by the other posters.

Do not add CYA until the ammonia is gone as it will just convert to more ammonia.
 
High FC will not have an effect on the CYA test. As you've noted, it will affect the pH test. High FC can have an effect on the TA test. Usually at high FC, you'll start with a green sample rather than a blue one after adding the R-0008. Then instead of the endpoint color change being the normal red it will change to yellow as the endpoint. If you know the FC is high, you can add a couple extra drops of R-0007 to eliminate this alternate color change (the R-0007 reagent neutralizes chlorine). I'm not aware of any issues with the CH test at high FC.
 
When I tested TA, it turned the normal blue color, so maybe I can assume that that reading was accurate and the only thing that was off was pH. That's so strange about the CYA. I am going to test the FC this morning and see what I come up with.

Is there a test I need to purchase to test ammonia? Or is it really just the adding chlorine and waiting ten minutes thing as Mr. Bruce posted above?
 
What FC level is too high for accurate pH readings? I'm at 10 FC right now. I should be able to get accurate pH, right? If so, pH is high and I need to get whatever I need to lower it before I can test the ammonia thing.
 
When did you last add FC and how much? If you are holding at 10 for more than 10 minutes, I'm pretty sure you don't have ammonia and can add CYA and start SLAMing.

edit to answer your actual question, with CYA = 0 I'd let FC fall to whatever it will naturally today, test pH, adjust as necessary, add CYA and then start SLAMMING. 10 is the number pH test starts being "off".
 

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So last night FC was at 0. I panicked and raised FC to 20 (I didn't calculate - just added 2 jugs of bleach because I was concerned about the algae). Now FC is at 10. I just tested. So based on what you've said, I should go ahead and test FC again pretty much now (it's been more than 10 minutes), and if it's still at 10, I can go ahead and add CYA and start SLAMing. Just reiterating so I'm not missing anything.
 
It looks like 2 gallons of 10% would get you to 15 FC, or lower with 8.25 so I'm pretty sure you don't have ammonia. Let FC drop just a little bit, check pH, add some CYA and you are off to the races!

How does the water look now?
 
Thanks Bruce. The water is crystal clear. Looks great, even after brushing, which sometimes if we have enough debris, etc., (we've got oak trees nearby), it will be slightly cloudy after brushing. But it looks perfect.

Any thoughts, then on why no CYA? That just seems really odd to me, when generally we've got some in our water at all times, and usually have to lower it nearing the end of the season due to using pucks. I'm just really puzzled.
 
Don't know. The first test I did as winter was transitioning to spring my CYA was the same as it was in fall. Then like 2-3 weeks later it was gone. I figured I had ammonia but nope. The CYA had just disappeared.

If you pass an OCLT, have <=0.5 CC and the water looks good you don't need to SLAM. You could just add CYA and go into maintenance mode.
 
So strange. Okay. I tested FC again and it's holding at 9.5. I think I'm going to just get the CYA and get that taken care of and then do an OCLT to make sure all is good. Thank you for the help. Here's hoping I don't have black algae as well.

Any thoughts on possible leaching from the pool surface due to low CH? And my thoughts are to increase CYA, then increase CH and see where TA ends up on its own before increasing that.
 
How low was your CYA at closing? CYA can be converted to ammonia by bacteria as was mentioned. It doesn't always stay as ammonia though. There is a complete nitrogen cycle where the CYA is converted to ammonia, then to other nitrogen species and can even go so far as to outgas as nitrogen. This is a VERY detailed and hard to read as a lay person, but it explains the whole cycle: Degradation of Cyanuric Acid (CYA))

Exerpt:

For every mole of CYA, 3 moles of ammonia are produced. This is equivalent to 10 ppm CYA producing 3.26 ppm ammonia (measured as ppm Nitrogen). Sometimes the ammonia will dissipate (probably outgas or get consumed by algae) over time, but any leftover ammonia would appear as unusual chlorine demand upon opening and take a LOT of chlorine to get rid of. For every 10 ppm CYA that is degraded and produces around 3 ppm ammonia, it would take nearly 30 ppm cumulative FC to get rid of (see this thread and this thread). One can buy an inexpensive ammonia test kit from a pet/fish/aquarium store.

<SNIP>

Annamox Bacteria: NH4+ + NO2- --> N2(g) + 2H2O

So each stage of bacterial degradation after the initial one to create ammonia lowers the chlorine demand as follows.
10 ppm CYA --> 3.07 ppm Ammonia nitrogen --> 24-30 ppm FC chlorine demand left to oxidize ammonia
3.07 ppm Ammonia nitrogen --> 3.07 ppm Nitrite nitrogen --> 16 ppm FC chlorine demand left to oxidize nitrite
3.07 ppm Nitrite nitrogen --> 3.07 ppm Nitrate nitrogen --> 0 ppm FC chlorine demand left
3.07 ppm Nitrite or Nitrate nitrogen --> Nitrogen gas --> 0 ppm FC chlorine demand left

So... if you're lucky, up to all the CYA could proceed all the way through the cycle and outgas as nitrogen, leaving you with no chlorine demand, but zero CYA. Most of the time the CYA to ammonia to nitrogen cycle is discovered somewhere in the region of ammonia to nitrogen gas conversion as that's perhaps the longest part of the cycle.
 
Very interesting! Thank you for that information. So in a way, it could be a good thing if it completed the process and now I'm just left with having to add back in CYA. It was at 40ppm when we closed the pool, so on the lower side for us, because previous years we've had it fairly high due to using pucks, etc. I try to limit puck usage when I'm in town as much as possible.
 
DanaSC said:
So strange. Okay. I tested FC again and it's holding at 9.5. I think I'm going to just get the CYA and get that taken care of and then do an OCLT to make sure all is good. Thank you for the help. Here's hoping I don't have black algae as well.

Any thoughts on possible leaching from the pool surface due to low CH? And my thoughts are to increase CYA, then increase CH and see where TA ends up on its own before increasing that.
Click to expand...
Yes it is possible. CH should be 250-350 to save your plaster.

JVTrain said:
CYA/ammonia stuff
Click to expand...
Awesome info Joel, thanks for that. That makes sense. I believe my CYA was around 30, will have to check my pool log to be sure.
 
This is really helpful info. I do believe I had a leaching problem before a couple of years ago. There was a dark spot on the bottom of my shallow end. After discovering low CH, I fixed that and the spot seems to have remedied itself. Am I imagining that or is that actually possible? Praying it's possible. So much to learn the hard way with pools, and I really don't want to ruin my plaster when it's only 5 years old. :)
 
Much of the chemistry foundation for this site is grounded in research and testing evaluated or performed by chem geek. If you're ever in the mood to dive deep and learn more about pool chemistry than you ever thought you could, look up most any chem geek post on TFP.
 

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