Expired liquid shock? Testing liquid shock for chlorine content

[etbrown4]

Liquid chlorine can be great for pools and doesnt add cya like granular shock, however it expires or weakens relatively quickly. Some writeups claim that in 6 months on the shelf, the 12% liquid shock will have little to no chlorine left. Buying in springtime is the most perilous if it is left from last year. So how can you be sure?

First look at the date code. The first two numbers are the year like 23. The next 3 numbers are the day, like 334 would be about Dec 1, of last year.

So that shock would be suspect, and might waste your time and money. I wouldn't buy it unless I had no better choice.

Tap water has a trace of chlorine, under 1ppm, so this test will slightly overstate chlorine ppm. That's a minimal effect. The test below is based on the ordinary shock ratio of 1 gal to 10,000 gals water.

Fill a 5 gal bucket with tap water. Add just over 1/3 (.038) of a teaspoon of your 12% bleach (but really a shy half tsp is close enough)

Read your recently bought test strips (old strips read wrong) or other testing means, and if your shock is fresh you should read about 12 ppm (or 10-15.) if you are using 6% bleach it should read about 6ppm so you will know it's full strength.

There's so much expired or weak shock out there especially at Walmart, this testing might save you lots of time and money! If it doesn't measure up, perhaps you can take it back.

 

[Newdude]

Read your recently bought test strips (old strips read wrong) , and if your shock is fresh you should read about 12 ppm (or 10-15.) if you are using 6% bleach it should read about 6ppm so you will know it's full strength.

You need a proper test kit to get actual values. Guess strips only give you some form of purple or green.

I feel your pain though. When my 2nd pool was filled it was going to be a week or so with no SWG and it took 3 stores and an hour and a half to get a couple jugs.

I had to wait 20 mins at Lowe's for the forklift kid to drop the only pallet they had, and it turned out it was way older than i would buy.

 

[Donldson]

Wow, this is... something.

Some writeups claim that in 6 months on the shelf, the 12% liquid shock will have little to no chlorine left.

What "writeups"? Sure, if left out in 100 degree weather in full sunlight that might be somewhat true, but on the other hand if stored in a cool dark place it will be nearly as strong. The rate of degradation also slows as the concentration decreases, you'll rarely find liquid chlorine that's completely depleted. That's why it doesn't "expire", it has a manufacture date.

Tap water has a trace of chlorine, under 1ppm

Tap water ranges from 0 ppm to 3 ppm usually. Mine has zero because it's not a municipal supply. A city nearby has cyanobacteria from the lake water so varies between 1 ppm in the winter to sometimes 3 or 4 ppm in the summer when the lake water gets extra thick.

Read your recently bought test strips

Seriously?

 

[Homebrewale]

My town uses chloramine to treat their water.

Maybe due to fast stock turnover, my local Walmart usually has the freshest chlorine.