Thanks! & question on CYA

[jgresham75]

First, a big thanks to all. I bought an AG and couldn't find anyone to put it in. So I did it myself. It was hard but it looks pretty good. Took a month but did it all with the help of TFP. I have used BBB for 3 weeks and water is still clear and wonderful! I will post pictures soon.

Now for my question. CYA was 0 at beginning and bought 4lbs of CYA from pool store. Was supposed to give 25 PPM per 10000 gallons. I have a 15x30 which has about 14000. It should have given me some CYA but my TFP test kit still says 0. I think I read in other posts that CYA under 20 can show up as 0. Is that accurate? Should I take sample to pool store for better testing? Also, I had some CC and so I shocked with 2 gallons of 6% Clorox. Should have put me up to 12-15. It put me up to 20ppm FC . That was Saturday. On Sunday had no CC but still had FC of 15. As of today had 5ppm FC and no CC. So that seems good. I am suprised FC stays so high if CYA was zero. I assume I should get more CYA. Pool will stay open til end of September in SE Virginia. Any suggestion on CYA and causes of high FC? Thanks in advance.

FC 5
CC 0
Ph 7.3
Alk 130
CA 50 (vinyl liner)
CYA 0 ?

 

[duraleigh]

I think I read in other posts that CYA under 20 can show up as 0. Is that accurate?

Pretty much. Your test stops at twenty so, if you have less than that, you will still be able to see the dot. That doesn't mean zero, it just means you have less than twenty. I would suggest another 2-4 lbs. That should put you around 35 which may be ideal and conserve your chlorine a little better.

Should I take sample to pool store for better testing?

Another opinion never hurts. That said, pool stores are infamous for poor test results. If your methodology is correct, your own results will most likely be more trustworthy than the pool store's.

2 gal of clorox would raise your pool by 8.6ppm. If you were expecting 12-15, your prior FC must've been around 5ppm. If the FC ended up twenty ppm, your original FC must've been higher (you were using gallons, not 1.42 gal jugs, right?)

Last, your FC is lasting because you are not at zero CYA...you're somewhere around 15-18ppm. Still, a 5ppm daily FC drop can be reduced even further with the addition of more CYA.....although I would not suggest more than an additional 4 lbs.....maybe even a little less.

 

[JasonLion]

Your CYA isn't zero, if it was you would have lost all your FC the first day. Based on your rate of chlorine loss I would guess CYA is more like 60 (or you don't get much direct sunlight on the pool). How long has it been since you added it? The CYA level can keep coming up for up to a week after you add some. Also, if you backwashed/cleaned the filter you could have lost some of it before it finished disolving. Assuming you didn't lose any and it all disolved you should of had CYA over 30, possibly as high as 55. My guess is that it was close to 20 when you tested it (which can read as zero), and is significantly higher by now.

Clorox normally comes in 96 oz and 182 oz jugs. Two 182 oz jugs would raise FC by about 20 in 9000 gallons. How deep is the water? A 3 feet deep 15x30 oval is 9000 gallons. 4 feet deep would be 12000 gallons.

 

[jgresham75]

Thanks for the help. My pool is 52" deep Sharkline. Their website says it is 14,800 gallons. I added the CYA Monday a week ago and have a cartridge filter but have not cleaned the filter since I put it in. So must should have gone into the pool. I will try adding 2lbs to start to get CYA up a little. In additions, I am pretty sure my bottles were the 1.42 gallons, not 1 gallon so that would have increased the chlorine higher than I expected. Thanks again for the help.

"I can also see the bottom of my pool!"

 

[Poseidon]

jgresham75,
Based on 13,464 gallons (15x30x4), 4 lbs of cya should have yielded 35 ppm. However, some cya products don't seem to yield the full amount, and some don't seem to yield any at all! I bought some cya and added what should have been 15 ppm, but got no measurable increase at all even after a week. I then added even more, still no increase.

 

[duraleigh]

jgresham,

Something's up with the math. Recheck your directions on the CYA label. Your results seem to indicate your instructions on the bottle are correct but the calculator Jason and Poseidon are using indicates about double ppm from the directions you posted.

 

[Poseidon]

jgresham,

Something's up with the math. Recheck your directions on the CYA label. Your results seem to indicate your instructions on the bottle are correct but the calculator Jason and Poseidon are using indicates about double ppm from the directions you posted.

I used two calculators. Jason's, and chem geek's. Got the same numbers both times. I was using a manually calculated 13,464 gallons (Jason's came up with 13,500 so close enough for govt. work

 

[JasonLion]

One other thought. Clorox brand bleach has been testing higher than the listed strength for a couple of people. I believe they ship it a little high so that after it has been on the shelf for a year it is still at the listed strength. The discount brands don't seem to be that generous.

 

[chem geek]

The calculators assume that the Cyanuric Acid is pure 100%. If they are cutting it so it's less than that, then the calculations will be wrong. However, I would expect the package labeling to indicate the percentage of Cyanuric Acid. If someone sees something significantly less than 100%, please let us know so we can update the calculators with options for different CYA "strength" (similar to what we do with bleach, chlorinating liquid and Cal-Hypo).