FC level increased double what I expected

[FloridaPoolGal]

Yesterday I added both CL and acid to my pool.

This is what I posted yesterday on another thread regarding my readings prior to adding anything:

FC 5.5
PH 8.0
TA 110
CYA ~60

These are my readings this morning:

FC 10.0
CC 0
pH 7.5
CH 375 (Note - This is slightly elevated from where we have been because we've tap water 3 times over the last 2 months due to evaporation. We've had windy weather with low humidity.
H2O 62 degrees

This is what I added to my approx. 22,000 gallon pool yesterday:

36 ounces of hydrochloric acid and the pH moved from about 8.0 to about 7.4-7.5
60 ounces of 10% chlorine and the chlorine moved from 5.5 to 10

My desire was to increase the FC from 5.5 to 7.5 so I added about 60 oz of 10% chlorine from Home Depot. I used the chart that came in my TF-100 kit to decide how much CL to add (56 oz) and I just went to the Pool Math Calculator and it also says 56 oz.

How in the heck did I end up with a FC level of 10.0? I purchased a case (4 gallons) of the 10% CL from Home Depot about a month ago. Yesterday, I finished the first gallon and started on the second gallon. If anything, I thought CL lost it's potency over time!

 

[ewkearns]

What are you using to test?

 

[pooldv]

There are really only a few options.

You're pool has twice as many gallons
You added twice as much bleach
The bleach is twice as strong as advertised
Test error either before or after addition
Math error in calculating the test results

Usually when I get an unexpected outcome it is my fault.

 

[ewkearns]

There are really only a few options.

You're pool has twice as many gallons

I think you meant half as many gallons.

You added twice as much bleach

That would be 1 whole bottle.

The bleach is twice as strong as advertised

That would be 20%. Whew! Can bleach fume? :joker:

Test error either before or after addition

My personal favorite.

Math error in calculating the test results

10 ml vs. 25 ml test..... hmmmmmmm? :?

Usually when I get an unexpected outcome it is my fault.

Me too, and I've had some doozies...

 

[pooldv]

LOL! Nice!

 

[FloridaPoolGal]

What are you using to test?

TF-100 test kit that is around 60 days old.

 

[ewkearns]

Testing error would be my suspicion..... but, OTOH, assuming the tests *were* accurate, it implies that your pool size is more like 11,000 (Cl) to 15,000 (pH) gallons. Is this the first time you have seen this, or are you just beginning testing?

You might want to play around with THIS some......

 

[FloridaPoolGal]

There are really only a few options.

You're pool has twice as many gallons
You added twice as much bleach
The bleach is twice as strong as advertised
Test error either before or after addition
Math error in calculating the test results

Usually when I get an unexpected outcome it is my fault.

The only explanation that makes sense to me is the jug of bleach (2nd one I've used out of the 4 jug carton) is actually double-strength. I just checked that at least the jug says 10% and it does. Jug 2 supplied about 80% of the bleach that I used. Using jug 2 of bleach is virtually the only change from the prior bleach additions to raise the FC so I guess that's where the finger gets pointed.

I have been testing the CL level every 4-5 days and I have added bleach from jug 1 when necessary. The FC level adjusted to the level that I expected. The second time I did the test this morning, I had my husband watch me because I couldn't believe the results. Today's results do track with what I measured late yesterday so I'm sure the CL level is 10. The Pool Math calculator said I should keep my FC level between 5 and 9 so I guess 10 is not too crazy. My hands smelled of CL after I got done futzing around in the water this morning. I've never experienced that before so something is different.

Is there any way to test the CL percent in a jug?

Has anyone ever had something like this happen? It's seems a little far-fetched that one jug of 20% bleach, labeled as 10%, would get mixed with 3 other jugs of 10% bleach. Although, who knows what the other 2 unopened jugs are like.

 

[ewkearns]

Is there any way to test the CL percent in a jug?

Yes, do a search, here on TFP, but it is kind of a pain and by the time you are diluting to the correct strength, you've lost a lot of accuracy.

Has anyone ever had something like this happen? It's seems a little far-fetched that one jug of 20% bleach, labeled as 10%, would get mixed with 3 other jugs of 10% bleach. Although, who knows what the other 2 unopened jugs are like.

You would be hard pressed to find 20% bleach, and even if you did, it wouldn't stay at that strength for long, at all.....

 

[FloridaPoolGal]

Too bizarre!

Sent from my SGH-M919 using Tapatalk

 

[kimkats]

Can you do a quick check of the date code on both of the jugs please? I would be curious to see if they are different.

Kim

 

[smforte]

When you used pool math did you chose the 10% bleach option or the 8.25? If you put in 10% bleach bu chose 8.25 in pool math that would account for the increase.....done that myself

 

[FloridaPoolGal]

Can you do a quick check of the date code on both of the jugs please? I would be curious to see if they are different.

Kim

Good idea!

Checked the date codes and they are identical. Looks the the bleach has a shelf life to 6-2016.

 

[FloridaPoolGal]

When you used pool math did you chose the 10% bleach option or the 8.25? If you put in 10% bleach bu chose 8.25 in pool math that would account for the increase.....done that myself

I just ran the Pool Math calculator with 10% (56 oz required) and then with 8.25% (65 oz) with a requirement to rasise FC by 2 ppm. The extra 9 oz wouldn't take me from a 2 ppm to a 4 ppm increase in FC.

 

[kimkats]

All out of ideas! When you go to add it next time put it at 12% and see how far it pushes the FC. Make sure the pump is running to mix it up. Wait about 30 mins. after adding to do the test.

Hey that made me think of something..........how long after adding the chlorine did you wait to pull the water? Do you always pull the water from the same spot? hummmmmmmm something else to think about.

Kim

 

[tim5055]

Good idea!

Checked the date codes and they are identical. Looks the the bleach has a shelf life to 6-2016.

Bleach/chlorine does not have a "shelf life", but does have a manufacture date. Generally thery are in a Julian Date format, something like XX16050XXX. In this example teh chlorine was manufactured the 50th day of 2016.

What is the exact code on your bottle?

Many times it will leave the plant at a higher concentration than advertised to account for reduction in % in storage and handling. If you get a really fresh bottle it can be higher than listed, but I don't think you will see a 10% bottle with 20% in it.

 

[pooldv]

You got me thinking Kim. Another possibility is the water wasn't fully mixed when the sample was taken. I like that option best.

 

[FloridaPoolGal]

All out of ideas! When you go to add it next time put it at 12% and see how far it pushes the FC. Make sure the pump is running to mix it up. Wait about 30 mins. after adding to do the test.

Hey that made me think of something..........how long after adding the chlorine did you wait to pull the water? Do you always pull the water from the same spot? hummmmmmmm something else to think about.

Kim

The test that gave me the FC level of 10 ppm was done at least 6 hours after the addition of bleach on Friday, 2/26. I tested Saturday morning, 2/27, and test FC of 10 ppm again. I just re-tested FC and it's at 9.5 ppm.

 

[FloridaPoolGal]

Bleach/chlorine does not have a "shelf life", but does have a manufacture date. Generally thery are in a Julian Date format, something like XX16050XXX. In this example teh chlorine was manufactured the 50th day of 2016.

What is the exact code on your bottle?

Many times it will leave the plant at a higher concentration than advertised to account for reduction in % in storage and handling. If you get a really fresh bottle it can be higher than listed, but I don't think you will see a 10% bottle with 20% in it.

Here are pictures of the bleach bottle to show date code and strength. I now see that the percentage is actually 11% and not 10%. The Pool Math Calculator said it would take 115 oz of 11% bleach to go from a FC level of 5.5 to 10.0. I put in 60 oz on Friday, 2/26/16.

 

[FloridaPoolGal]

I rechecked the FC level about 1 pm today, Sunday, 2/28/16:

FC 9.5 Down .5 from yesterday
pH 7.5 Same as yesterday

The pool looks great. The water is clear and sparkling!

The cat is still drinking the pool water. I hope it's not bad for her but there's no way to keep her from drinking it. Making her stay inside on a beautiful day is not an option because she would meow for hours and scratch at the door and drive her humans CRAZY!