Question about dosing for liquid chlorine

[BigOrangeSpa]

Hey ya'll,

I just recently switched over from Dichlor to bleach after reaching 30 CYA. I bought this liquid chlorine from Lowes: https://www.lowes.com/pd/Pool-Essentials-1-Gallon-Liquid-Pool-Chlorine/5001527059. According to the date on the bottle, it was produced in August so it shouldn't be expired? It's 10% strength.

I'm using the PoolMath app to calculate how much to add to raise FC. I'm noticing that after adding the LC and letting it circulate for around 30 minutes, it's usually pretty far below where I set my target in PoolMath. For example, earlier I tested and my FC was 2.5. I set the target to be 6 and when I tested 30 minutes after adding the amount PoolMath told me, it was only reading 4.5.

Is 30 minutes the right amount of time to wait? Do you think I just got a bad bottle and it's degraded? Should I lower the strength % in PoolMath until the the amount it gives matches the FC I'm seeing?

 

[drsipe]

Unfortunately, liquid chlorine begins to degrade quickly, here is a chart to show how quickly it does degrade.

Breakdown of Bleach Over Time by Storage Temp - Further Reading

www.troublefreepool.com

The 30 minutes of circulation is sufficient time to test.

Additions of chlorine are usually not simple math, there are many factors which will effect your final chlorine levels, any biologicals in the water, and the actual percentage of sodium hypochlorite in the bottle.

 

[Mdragger88]

Try testing a little sooner. 5-10 minutes is plenty in a spa.
If you’re still getting the lower results then adjust your strength % in poolmath to match up with your results going forward with that bottle.
Fresh stuff would be a month or less old.
Also avoid buying where they store it out in the heat or the sun as that degrades it faster.
As we roll into the winter with pool season ending you may need to source plain unadulterated household bleach instead if you can’t find fresh dedicated pool chlorine.
So long as it has no fabric conditioners (cloromax), no scents, and isn’t splashless.
No sense in paying more for dedicated pool stuff if it’s no stronger than household stuff.
I sometimes get generic 7.5% from dollar general or chloralen brand (the plain concentrated one) from Walmart or aldi, its 7-8%. I believe Home Depot has a house brand that is totally plain as well.
Some are only 3-5% so read the labels. If no % is listed it’s usually quite low.
When in doubt about extra ingredients look up the sds sheet.

 

[BigOrangeSpa]

Thank you! I tested 5-10 minutes afterwards and it is still reading quite a bit lower. I'm going to go ahead and start decreasing the percentage in PoolMath by 1 each time I add it until it matches. Appreciate the help and the explanation of how bleach degrades. I'll keep that in mind. It was definitely in the outdoor section at Lowes, and who knows how long it sat there during the summer.

I'll check about the generic 7.5% at dollar general and see if they have it here.

 

[JoeSelf]

You can use effects of adding to back into the difference between the two tests.

 

[Mdragger88]

What Joe means is in the effects of adding tab (in the hamburger menu)
if it gave you a 2 ppm rise for example play with the % until it shows it yielding a 2ppm rise. Then use that as your % going forward until you use it up.

 

[BigOrangeSpa]

Oh clever! I did it the hard way. I'll try that technique next time I get a bottle that isn't working at the full strength. I found that 7.5% matches up perfectly with the amounts I'm adding and FC I'm seeing. Thanks all!

 

[elbow]

My favorite is when my local Ace overbuys cases of chlorine with an April date at the beginning of the summer and then tries to unload them all in September by putting them in front of the store, directly in the sun, at no discount.

 

[SJPoe]

My favorite is when my local Ace overbuys cases of chlorine with an April date at the beginning of the summer and then tries to unload them all in September by putting them in front of the store, directly in the sun, at no discount.

Nooo ! Stores wouldn't do something like that right ???

Oh. wait....

 

[phonedave]

I am going to ask the obvious question - is your spa size set correctly in the pool math app?

 

[BigOrangeSpa]

I am going to ask the obvious question - is your spa size set correctly in the pool math app?

Yep!