chlorine off after immediate addition

[chris4150]

Hello all,

Its been a while since Ive posted but Im always visiting and reading. Trying to figure out something with my chlorine recently. Here are my numbers via TF-100 and then Ill post the question.

FC .5
TC .5
PH 7.8
TA 60
CH 130
CYA 30
water temp 71

Ok, I wanted to raise my FC to 4 ppm and confered with the pool calculator which suggested that I add 3 quarts of liquid bleach based on my current CYA level of 30. After adding the recommended dose and circulating the water for approximately 45 minutes I checked the FC, via TF-100, for a base line and discovered that the FC was at 2 ppm. My question, should the chlorine have dropped from the attempted 4 ppm to 2 ppm that quickly? The test was conducted in the evening in order to verify if I would lose more than .5 ppm over night. The next morning I obtained a reading of 2 ppm. Believing that I did not have any issues based on my FC levels holding over night, Im still wondering why I didnt get a 4 ppm reading when I first added the chlorine as suggested to raise my initial chlorine from .5 to 4 ppm via the recommened dose. Your replys are greatly welcomed.

Chris

 

[Pacifica]

You need to raise your cyanuric acid to about 50-60 ppm for the upcoming summer. My guess is that the chlorine dropped out with your CYA only being 30 ppm. Just remember to add your conditioner (CYA) slowly because you can't remove it from the water unless you drain it off. Raise it by 10 ppm each time until you reach 50-60 ppm. Hope that helps.

 

[chris4150]

Thank you for the reply Pacifica,

If the chlorines initial drop was due to the CYA being at 30, would it have continued to drop over night or is it my understanding that at a CYA level of 30 the chlorine held at 2 ppm in relation to the CYA of 30 since I had no further loss over night and into the morning?

Chris

 

[chem geek]

There was probably a lot of loss during the day if there was direct sunlight. However, with the FC low before you added 4 ppm, nascent algae growth could have started, even if not visible, so you could have had some overnight loss as well in addition to higher losses during the day. To check the overnight loss, you need to test with the sun mostly off the pool in the evening and then again in the early morning. If you find > 0.5 ppm FC overnight loss, shock the pool to kill off the nascent algae.

 

[duraleigh]

Good Morning, Chris,

Like Richard, I suspect you had some organics (algae) in the pool. It's not clear exactly what time of the day you dosed with chlorine.....my assumption is after the sun was off the pool.

I suppose that 45 minutes may have been a little brief for thorough mixing of the FC (you may have taken the test sample from a "weak" spot) but my experience in my pool indicates 45 minutes is probably enough (although we generally say an hour....just to be safe.

I would conduct the overnite FC loss test again but this time without adding chlorine. Simply do the FAS/DPD FC test (CC's if you want, too) after the sun is off the pool and then again before the sun strikes the pool. A loss of greater than .5ppm would indicate you still have some organics to take care of.

It does appear you may be running your FC a tad low so that would add to the possibility that some algae has crept in.
I would be somewhat puzzled by that test in my pool, also. To have lost 2.5ppm in FC in 45 minutes seems a little bit of a stretch......possible, but a stretch. You may just have to chalk it up to the vagaries of testing but I would repeat the overnight test toconfirm the results.

How does your water look? Is it crystal clear?

In your part of the country, a higher CYA value around 50+ seems like a good choice. Have you intentionally picked 30ppm?

If you decide to increase the CYA, you obviously understand how to use the calculator. I would suggest you dose to the desired level. Your accuracy and understanding are very good. The test is plus or minus 10ppm, anyway.

Let us know what you find out on that second overnight FC test.

 

[JasonLion]

It seems most likely that the bleach you are using is not as strong as you think it is. Bleach loses strength as it ages, especially if it is stored at high temperatures.

 

[chris4150]

Thank you to all that replied.

Ill try to respond to the questions in summary.

The addition of the bleach and the subsequent test was conducted in the evening with minimal or no direct sun light on the pool. The follow up test was conducted at approximately 9 A.M. The follow up test indicated no over night chlorine loss. My pool water is clear, but thats not to say trace algae is not present. Ill conduct another over night test tonight without adding any additional chlorine. My CYA of 30 was a result of adding conditioner per the instructions with the goal of achieving somewhere in the 30 to 40 range. Given the amount of sun and heat we get here in Houston Ill propbably take the advice and bump it up to 50. While Im at it I need to raise my CH and TA. They are a bit on the low side. I think my enemy in regards to my PH and TA is I have a spill over spa, unfortunately, I dont have much of a way to combat this. Again, thank you to all the replied and Ill post tomorrow the next set of readings.

Chris

 

[duraleigh]

It seems most likely that the bleach you are using is not as strong as you think it is.

Doh! (insert Homer icon)

 

[frustratedpoolmom]

Hey Chris
I'd suspect the bleach - sounds like you were doing the test correctly (we're looking for an overnight loss of greater than 1ppm tho ). It is possible you "nipped something in the bud" and it consumed the bleach as you were adding it, but that's less likely than a weakened % of bleach, IMHO.

 

[chris4150]

Hello Frustrated,

It may could have been the bleach. It was the last bottle of my last purchase some months ago. The bleach is stored in the laundry room inside the residence on top of the dryer. Since its inside the residence the laundry room is climate controlled as the rest of my house. I have since purchased new bottles of bleach (182 oz) and will run the test wit the recently purchased bottles.

Talk to you then,

Chris

 

[chem geek]

I think my enemy in regards to my PH and TA is I have a spill over spa, unfortunately, I dont have much of a way to combat this.

Just remember that if your pH tends to rise due to the increased aeration from your spillover spa, then you might not want to raise the TA very much and could in fact keep it at 60 ppm if that's what it takes for the pH to be more stable. If you do keep a lower TA, you can raise the CH to compensate to get the saturation index closer to zero. You could also consider using 50 ppm Borates as an additional pH buffer (in addition to the lower TA target).