Liquid bleach didn't increase FC by what I was expecting

[TobyB]

Hi,

I am new to the TFPC method and aimed to raise my FC from 1.61 to 7 by adding liquid chlorine/bleach. I had a CC 0f 0.74 before adding the bleach and when I tested it 2 hours later I had a CC of 0 and a FC of 2.24.

My water temperature is kept at 42℃ and my test results before adding bleach were:

• FC - 1.61
• CC - 0.74
• PH - 7.45
• TA - 68
• CYA - 71

MY CYA is a bit high as I was using trichlor tablets while waiting for my 15% liquid chlorine delivery and I let my FC drop in recent days as I didn't want my CYA to increase too much.

Using the PoolMath app it suggested I add 43mm of my 15% bleach to increase FC to 7. Would the less-than-expected increase be due to the CC present in my water or could it be due to a bad batch of bleach?

Thanks in advance

 

[MITBeta]

I would try again, but test 15 minutes after you add the chlorine.

 

[wireform]

To be 100% sure do a OCLT Overnight Chlorine Loss Test .The mere fact you let the FC drop low could be the beginning of algae even though you don't see it.

 

[TobyB]

Hi,

Thanks for your responses.

I had actually added another 45mm of bleach at 15% before writing the post as the FC was low whether it was due to something using it or a bad batch of bleach.

I will test again tonight and try the OCLT test as well to see if something could be using it up.

 

[TobyB]

So I tested the free chlorine again this evening just before sunset and it was 6.0 after the additional 45mm bleach.
When I was testing, the water wasn't clear anymore but had a cloudy haze to it. From my reading, I suspect this may be due to calcium carbonate from the temporary increase in PH from the bleach.

If hypothetically it was a bad batch of bleach and isn't 15%, would it still have the same effect on increasing PH before the chlorine is used up or would the PH not increase by so much?

I'll test again first thing in the morning to measure the OCLT

 

[TobyB]

Hi again

So I tested first thing this morning and still had a FC level of 6 and a CC level of 0. As it is a hot tub it is covered when not in use but would one normally expect it to go a whole night without any chlorine demand at all (I know this is what we aim for but I would have thought there would normally be a tiny bit of demand)?

When testing the water, it was still cloudy and so I think yesterday adding in total 90mm of liquid chlorine for a 1000 litre tub must have had an effect on the PH. It was my first time adding liquid chlorine but maybe I should have reduced the PH first?

Anyway would this confirm that the bleach isn't the 15% it was sold to me as, if there is there is no chlorine demand overnight and adding the bleach didn't increase the FC to my expected levels?

Thanks

 

[ajw22]

Bleach aka liquid chlorine begins to degrade the moment it is bottled. In manufacturing they may make it 17% so it is at least 15% when you get it. Or the 15% may degrade to 10% by the time you are pouring it into your water.

Breakdown of Bleach Over Time by Storage Temp - Further Reading

www.troublefreepool.com

It sounds like you may have had some algae in the water that the initial doses of chlorine cleared. I would not be concerned about minor variances day to day. Watch the overall trends.

It does not matter if you add chlorine or acid first but add them 15 minutes apart. But test your FC and pH before adding either chemical.