Old chlorine

[Ron55]

I have some old chlorine in my garage. I purchased it last year at the end of the season and never used it and was planning to discard it as I purchased new liquid chlorine right before Covid hit here. I ran out of that chlorine and was wondering about using last year's batch.
It was manufactured mid September 2019 so almost a year ago. 12.5%
While I realize it's effective is severely limited perhaps to nothing, is there any danger in putting it into the pool?
I'm trying to avoid a trip to the store as I have health concerns.

Thanks for your help.

 

[mknauss]

You can use it. Mostly salt water. Might have 2-3% sodium hypochlorite.

 

[TheDeuce]

If you measure your add and get an FC reading before and after could one theoretically determine the actual concentration? Assuming it's a night time add to cancel out sun effects AND assuming you don't have anything in the water consuming FC.


m.

 

[jseyfert3]

If you measure your add and get an FC reading before and after could one theoretically determine the actual concentration? Assuming it's a night time add to cancel out sun effects AND assuming you don't have anything in the water consuming FC.


m.

For sure, it's easy, if you know the pool volume is correct, and the chlorine is well mixed after adding.

Say PoolMath says you need x amount of 12.5% chlorine to raise FC by 4 ppm, but you add x amount and the FC only goes up by 1.5 ppm. 1.5/4 = 0.375. Multiply 0.375 by 12.5% and you get 4.7%, which would be the actual concentration of sodium hypochlorite remaining. Then for the remainder of the old chlorine, put 4.7% into Poolmath.

 

[red-beard]

You can test the chlorine. Add 1 drop to 500 ml of water of a known FC level.

1 drop - 1/20th of a ml of water

Test the pool water to get a known FC level
Take 500 ml pool water and add 1 drop of the bleach
Test the 500 ml water for FC. Subtract your first FC reading. This net FC level is the % bleach.

I've been doing this with my bleach bottles from Home Depot, since the batch turned out to be 2-3 months old. My 10% bleach is around 6-7%.

 

[Wobblerlorri]

I was in the same situation as you, had leftover bottles of chlorine from last year, about 9 of them. I used Pool Math to back calculate the strength of the acid, found out my 10% chlorine had degraded to 6%. Other than having to use more to dose, it's perfectly safe to use.

 

[TheDeuce]

You can test the chlorine. Add 1 drop to 500 ml of water of a known FC level.

1 drop - 1/20th of a ml of water

Test the pool water to get a known FC level
Take 500 ml pool water and add 1 drop of the bleach
Test the 500 ml water for FC. Subtract your first FC reading. This net FC level is the % bleach.

I've been doing this with my bleach bottles from Home Depot, since the batch turned out to be 2-3 months old. My 10% bleach is around 6-7%.

I had been thinking of how one could use this approach although I thought one would start with distilled water (FC=0). I just didn't know how the change in FC per unit bleach added could be converted to ppm. Thx for the explanation!



m.

 

[red-beard]

Distilled water would be best. And not too expensive. But I don't have much on hand. I tried tap water, but we use chloramines for sanitation (2 PPM!), which I think screwed up the test. Using pool water after testing it works fine and is cheap and plentiful.