# Thread: measuring bleach strength

1. ## measuring bleach strength

Is there an easy way to test the strength of bleach?

I figure if you dilute it 10000 times then you can test using the conventional way.
But whats a good rule of thumb to do the dilution?

For whatever reason my last round of bleach from the pool store didn't seem to cut it.

Sorry if this is a redundant thread. all my searches turned up as testing the pool water not the actual bleach

2. ## Re: measuring bleach strength

nope...valid question...easiest guage is using the pool volume. One gallon of 6% bleach should raise the FC in a 10K gal pool by 6ppm. One gallon of 12% = 12ppm, etc...so if you are using 6% bleach in a 11k gal pool, you should get an FC boost of about 5.5ppm +/- 0.5ppm, after adding one gallon, assumming it's a "fresh batch"

4. ## Re: measuring bleach strength

thank you.
My 10.5% bleach measured (using my pool volume) to be 8.5%

Do the pool stores store their bleach in translucent plastic towers outside the store?
I wonder if I just have old bleach since its winter time.

5. ## Re: measuring bleach strength

It can be done by dilution fairly easily with a set of digital scales. I set the scales to zero (grams) with an open container on. Then put in about 3-500 grams of clean water, add 100 g of bleach and top up to 1000 g. That's dilution of 1/10. Stir and take out and save a plastic cup full.

Empty and rinse the container, put back on the scales and repeat the process, this time adding the 100 g from the plastic cup. This dilutes to 1/100. Discard/rinse plastic cup, take another cup full. Do twice more - four in total - and that's 1/10,000 (as the bleach is already n/100 dilution this brings it to ppm strength). A final stir and test the result with the pool kit.

If my maths is rubbish I'm sure someone will correct my foolishness.

The reason I do 100 g to 1,000 g and add the 100 g in the 'middle' of the dilution is to lessen the effect of slight inaccuracy. You also need clean un-chlorinated water to do the dilution.

(Edit: posted before I read Ohm_Boy's link, which says much the same thing.)

6. ## Re: measuring bleach strength

Just for completeness: 1/2 tsp 6% bleach in 4 gallons* unchlorinated water should read as 10ppm.
(That's approx 6000:1 dilution. Measuring the 1/2 tsp precisely is the hardest part.)
--paulr

* U.S. not Imperial, not that I think anyone really still uses Imperial gallons, I'm just showing off

7. ## Re: measuring bleach strength

< not that I think anyone really still uses Imperial gallons....>

Oh I don't know, old boy, still a few of us left in the old Empire.

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