Weird CYA readings

tkrunche

Member
Aug 22, 2018
16
Shakopee, MN
Hi--

I opened the pool just fine. Crystal clear, still had a bit of chlorine in from the winter. Six days ago my numbers were:
FC: 3.5
CC: 0
pH: 8.0
TA: 225
CH: 550
CYA: 60

I added some Muriatic Acid (first time tried this brand, Jasco Green Muriatic Acid from Lowes) to bring the pH down. I also added about 3lbs of CYA in a nylon in the skimmers. Then we had some family emergencies and I was away from home for a few days and yesterday the pool was cloudy. I did a few tests and the results were

FC: 0
pH: 7.1
CYA: 0

I know the only way to decrease CYA is splash out or diluting. We have not swam and there was about 3" of rain (but we have an automatic cover so the pool probably didn't get much water in it). Why would CYA be reading 0? I did the test three times all with the same result. Could it be that within 5 days my testing chemicals stopped working? I bought the test kit (Taylor) last year so all chemicals are about a year old, but they seemed to work fine when I got my numbers 6 days ago.
 

IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,177
Milwaukee, WI
With 0 FC and 0 CYA after previously having both I'm concerned that your FC fell too low and you got some CYA-eating bacteria in the pool. They convert the CYA to ammonia which burns through FC like crazy. You can get rid of it but with a lot of chlorine.

I would recommend adding 10ppm worth of liquid chlorine, mix for 15 mins, test and see what your FC is and let us know. Don't add more CYA until we've ruled this out - if you do have this bacteria, then it will just turn it into more ammonia. If you do have it we need to burn through all of the ammonia so that the FC can kill the bacteria.
 

tkrunche

Member
Aug 22, 2018
16
Shakopee, MN
Ok, so was able to come home for a bit. Checked and there was 0.5 CC (still no FC or CYA). I added 3 gallons of 10% bleach which should have brought me to a bit above 10ppm. Waited 15 min and then it was 0.5 FC and 0.5 CC. So I must have that bacteria you speak of? Should I do the slam? Do I need CYA before I slam (although I suppose that's not possible since I have bacteria that eats it up.)?
 

IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,177
Milwaukee, WI
Sure sounds like it, though the lack of CC is a bit odd. Still, something is eating the FC.

Two options - water exchange or invest heavily in bleach. The bleach method is pretty much just what you did. Keep dosing back to 10ppm and testing after 15 mins of mixing. When it finally starts to hold FC then you want to add the CYA, not before.
 
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PoolGate

Gold Supporter
TFP Guide
Jun 7, 2017
4,694
Damascus, MD
If you can get an ammonia test kit like from an aquarium you'll have an idea of when your done adding chlorine. I've done 2 pools with ammonia it'll take near 50 gallons to clear it. For now keep adding chlorine maybe 5 gallons at a time and waiting 15 minutes until you get a reading.
 
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tkrunche

Member
Aug 22, 2018
16
Shakopee, MN
Ok, sorry I'm not responding quick. I have a kid in the hospital so I haven't had time to get to the pool consistently. I'm home tonight so I tested the water for the first time since my last post and I got <0.5 FC (I did 10 ml sample so it was just the tiniest bit pink, and probably wouldn't have needed that whole one drop, I'd estimate 0.2). and 0.5 CC. I dumped in 3 gallons of 10% bleach and tested it 15 min later. This time I got 0.4 FC and 2.4 CC. So, I just keep dumping in 3 gal at a time until it holds FC? Do I need to worry about that CC?

Also, I have an ammonia test from a fish tank and the colored pad reads between the 0.5 and the 3.0 (that seems like a giant leap from one color pad to the other?!).

Thanks
 

IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,177
Milwaukee, WI
Yep, keep dumping in FC, enough to get to 10ppm and testing after 15 minutes. Once you get a reading you can add CYA and get to doing a SLAM. The CC will go away with sunlight and the SLAM once the ammonia is gone.
 

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
12,465
Houston, Texas
You want to keep more than 1/2 your FC after 15 minutes, so once your test reads 6 or more you go into regular slam mode and it will be safe to add CYA. While in slam mode only add enough CYA to hit 30 ppm.
 

tkrunche

Member
Aug 22, 2018
16
Shakopee, MN
The saga continues. I've been pouring in gallon after gallon of liquid chlorine, enough to get to 10, and 15 min later it's gone. Then I had my dad working on it since I was gone again and he poured in a bit of CYA....probably up to about 40ppm. We can't find liquid chlorine anywhere (thanks Covid) so we are now using dichlor (Brand is Zipchlor - which I know is going to increase CYA even more). It still won't hold FC. Last night I put in about 8 pounds of Zipchlor which, according to the pool math app, should have bumped my FC up to around 20ppm. This morning I tested and it's at 1.5 FC (0.5 CC, 7.1 pH, 75 CYA). What do I do? Keep dumping in Zipchlor? Is there a better alternative to liquid chlorine I can't find? I usually just buy it from Walmart but there isn't a Walmart within 100 miles of me that has it in stock. Zipchlor is expensive at about $150 for 25 pounds and at the rate my pool is eating it up I'm going to go broke :) So, just wondering if I just keep dumping it in or if there is anything else I can do.
 

PoolGate

Gold Supporter
TFP Guide
Jun 7, 2017
4,694
Damascus, MD
The saga continues. I've been pouring in gallon after gallon of liquid chlorine, enough to get to 10, and 15 min later it's gone. Then I had my dad working on it since I was gone again and he poured in a bit of CYA....probably up to about 40ppm. We can't find liquid chlorine anywhere (thanks Covid) so we are now using dichlor (Brand is Zipchlor - which I know is going to increase CYA even more). It still won't hold FC. Last night I put in about 8 pounds of Zipchlor which, according to the pool math app, should have bumped my FC up to around 20ppm. This morning I tested and it's at 1.5 FC (0.5 CC, 7.1 pH, 75 CYA). What do I do? Keep dumping in Zipchlor? Is there a better alternative to liquid chlorine I can't find? I usually just buy it from Walmart but there isn't a Walmart within 100 miles of me that has it in stock. Zipchlor is expensive at about $150 for 25 pounds and at the rate my pool is eating it up I'm going to go broke :) So, just wondering if I just keep dumping it in or if there is anything else I can do.
Adding CYA was a big mistake. You just fed the bacteria and exasperated your problem. Get an aquarium ammonia test kit! You need to know how much ammonia you have and your progress adding chlorine. As I said above, it took 50 gallons to clear those pools of ammonia. How many have you added so far? That CYA you added probably means an additional 30-40 gallons of bleach.

The other option is to completely drain your pool and refill.
 
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splashpad

Bronze Supporter
Aug 2, 2017
2,708
SE Kansas!
The saga continues. I've been pouring in gallon after gallon of liquid chlorine, enough to get to 10, and 15 min later it's gone. Then I had my dad working on it since I was gone again and he poured in a bit of CYA....probably up to about 40ppm. We can't find liquid chlorine anywhere (thanks Covid) so we are now using dichlor (Brand is Zipchlor - which I know is going to increase CYA even more). It still won't hold FC. Last night I put in about 8 pounds of Zipchlor which, according to the pool math app, should have bumped my FC up to around 20ppm. This morning I tested and it's at 1.5 FC (0.5 CC, 7.1 pH, 75 CYA). What do I do? Keep dumping in Zipchlor? Is there a better alternative to liquid chlorine I can't find? I usually just buy it from Walmart but there isn't a Walmart within 100 miles of me that has it in stock. Zipchlor is expensive at about $150 for 25 pounds and at the rate my pool is eating it up I'm going to go broke :) So, just wondering if I just keep dumping it in or if there is anything else I can do.
Adding CYA is feeding the bacteria, which is producing ammonia, which is depleting the chlorine faster than you guys are adding it. Please no more CYA (stabilizer) until the FC showing over 6 at least 15 min after adding a Fc/10 dose per PoolMath
 

tkrunche

Member
Aug 22, 2018
16
Shakopee, MN
Yes, I knew the stabilizer addition was a mistake, I must not have made it clear for my dad to not do that. What can I use instead of liquid chlorine? I can't find any and I know there is CYA in dichlor.
 

PoolGate

Gold Supporter
TFP Guide
Jun 7, 2017
4,694
Damascus, MD
Yes, I knew the stabilizer addition was a mistake, I must not have made it clear for my dad to not do that. What can I use instead of liquid chlorine? I can't find any and I know there is CYA in dichlor.
Have you called your local pool stores? They usually sell higher concentration like 10-12% which is equivalent to 2 of the local supermarket bleach.

Do you have a high water table? Have you ever drained your pool?
 

tillmac62

Well-known member
Sep 30, 2019
73
Gaffney, SC, United States
Can you drain the pool? Cal-hypo as a chlorine source in your case is a poor option due to your CH level. Dichlor and trichlor each add CYA, which is adding to your problem. You either have to drain the bacteria away or kill it.
 

tkrunche

Member
Aug 22, 2018
16
Shakopee, MN
The water table isn't higher than our pool (no water when they dug down and installed it). I'd rather avoid draining the pool. That'd be even more expensive than bleach I think.