# Thread: Measuring liquid chlorine/bleach by weight.

1. ## Measuring liquid chlorine/bleach by weight.

I get tired of figuring out what 38oz is, or 41 or what have you. I'm a very precise person, even though I know we aren't "making rocket fuel" here, I still want to be as accurate as I can with dosing.

So I figured I'd weigh it when it's not a standard measurement marked on my Pyrex vessel.
I know that bleach weighs more than water, as it is more dense due to the chlorine molecules. Not sure on the NaOH/Lye, I would imagine so.

Through my research, I have found that a 6% solution of sodium hypochlorite weighs 1.08g/ml.
Assuming this is correct, is it ChemGeek or someone else?

I have performed the following math /w the help of Google Calc. I'm not a math expert, but I can hack it, so if any of this is expressed incorrectly in it's written form, I do apologize. Please feel free though, to correct any formatting errors, but still, I have to be able to understand it when I read it. I don't want an equation that takes up part of a plexi marker / chalk board.

My notes:
Code:
```1ml of 6% Sodium Hypochlorite solution = 1.08grams

29.5735296ml = 1oz.
Xnum. Ml x 1.08g =  31.939411968g
1oz. CL in Vol by weight = 1.12663/oz

To determine weight per vol oz. of bleach to be
measured:
-Multiply number of oz. in volume by 1.12663```
Any help would be awesome, thx.

2. ## Re: Measuring liquid chlorine/bleach by weight.

I am just going to point out that many people do not even use measuring cups ... and just estimate to the nearest 1/4 of a jug. However, that obviously will not work very well on the smaller pools (in your case 1/4 of a 182 oz jug of 6% is a 5.4 ppm FC rise ... and estimating 1/8 of a jug might be tough for normal day to day activities).

So I would suggest that you not worry too much about getting any more accurate than the nearest cup of bleach. 1 cup (8oz) = 1ppm in your pool. So by rounding to the nearest cup, you should be dosing within 0.5ppm of your target.

Why make it more difficult than it needs to be right ... it is supposed to be Trouble Free

BTW: Using your numbers, you just have to take: # oz bleach * 31.9 = # grams bleach

3. ## Re: Measuring liquid chlorine/bleach by weight.

Originally Posted by jblizzle
I am just going to point out that many people do not even use measuring cups ... and just estimate to the nearest 1/4 of a jug. However, that obviously will not work very well on the smaller pools (in your case 1/4 of a 182 oz jug of 6% is a 5.4 ppm FC rise ... and estimating 1/8 of a jug might be tough for normal day to day activities).
Very true, if I had a huge pool, which I want some day!!
..Then I wouldn't worry so much about it, but the less water volume, the more response to slighter changes in chemistry. Yes, I understand that's to a point.

Originally Posted by jblizzle
So I would suggest that you not worry too much about getting any more accurate than the nearest cup of bleach. 1 cup (8oz) = 1ppm in your pool. So by rounding to the nearest cup, you should be dosing within 0.5ppm of your target.
I duunnnnoooo, my actual diagnosed OCD says otherwise.
I'm really not going to use it for day to day dosing though, mainly I just want to get a really tight handle on how much bleach is raising it by how much PPM. Since I'm fighting with an OTO kit (for another week or 2) that's lying to me, I want to reign it in with some experiments. Slightly underdosing, seeing what it goes to, etc..
I'm just being a nerd.

But yeah, for day/day dosing, I'm just filling up a big huge Pyrex, sight leveling it and calling it a day.

BTW, these Pyrex vessels seem to have a slightly lower, somewhat slanted line on the left of say 1cup, than the line to the right that says 8oz. which is a little higher. I'm presuming the left side is for dry & the right is wet, or is it vice versa?

Originally Posted by jblizzle
Why make it more difficult than it needs to be right ... it is supposed to be Trouble Free
Oh sure, I want it as TFP as possible for day/day stuff. But that doesn't change the fact I'm a nerd and want to know what's going on with everything I do. It's fun!! HEHE

Originally Posted by jblizzle
BTW: Using your numbers, you just have to take: # oz bleach * 31.9 = # grams bleach
Yeah, I see the shortcut, in fact that's what I just did /w 30oz. was to do it the way you said. I just mapped it all out & wrote it down so it'd make sense to me if I later needed to reference it, or question how I got there. You know, "showing your work". Gosh I hated that in school!! I got the answer right, what do you "teacher" care? LOL

4. ## Re: Measuring liquid chlorine/bleach by weight.

You can't be all that precise with dosing, there are too many unknowns. Nor is there any point in trying to be. The strength of the bleach is going to noticeably different from batch to batch, certainly by more than the error inherent in using a measuring cup. The goal is to measure your level, make an approximate adjustment, then measure your level again the next day and repeat. The repeated daily measurements provide the precision and repeatability, while the actual dosing varies a fair bit. Any error in todays dosage gets fixed tomorrow, and so on down the line.

5. ## Re: Measuring liquid chlorine/bleach by weight.

Makes good sense.

I was wondering about the variability in batches of bleach, even if fresh. Transport temperature, how long it sat on the doc in the sun, aeration from sloshing, etc...

I always try to get the bleach with the farthest out expiration date printed on it. It's always a year out, the stuff I get.

Just as well, cause measuring by weight is a bit of a pain, you go over, you go under, it's a drag. HAHA

6. ## Re: Measuring liquid chlorine/bleach by weight.

There are also errors in calculating the pool volume. As for the 1.08 g/ml density of 6% bleach, that is in fact what I use in my spreadsheet and that is what Clorox had in their MSDS. It also implies a 5.715% Available Chlorine which is the weight % of chlorine and a Trade 6.172% which is the volume % of chlorine so 1 gallon in 10,000 gallons would produce 6.172 ppm FC. The density of 12.5% chlorinating liquid is around 1.16 g/ml.

7. ## Re: Measuring liquid chlorine/bleach by weight.

My pool volume should be correct, as it's an Intex and they have it in their specs, so long as you fill it to the bottom of the inflatable ring. So I'm probably no more than 50-100gal off, as I like the water level a bit high.

I just topped it off and put it almost right on the money, so it should be very very close.

But yeah, I hear ya, with free form pools and the like, unless you actually meter it, there's really no way of knowing to a spot on number.
Shame there isn't a laser we can float on the water that'll shoot beams at a various tangents to tell us the exact volume of the area at the specific height of the water level at that time.
I see no reason why something like that wouldn't be doable and I bet it exists in manufacturing somewhere. Probably be too expensive, something we'd have to rent I'm sure.
But it'd be a great tool!!

So if it says 6% Sodium Hypochlorite on the bottle, is that what we use in the calculator, not the FAC or trade rating that you listed, which is less & more than 6% respectively?

Thx.

8. ## Re: Measuring liquid chlorine/bleach by weight.

The Pool Calculator uses the by weight % (the number most commonly listed on the bottle). But since getting exact results is both impossible and unimportant, using any of the three is equally good.

9. ## Re: Measuring liquid chlorine/bleach by weight.

OK, Cool!
I'll stick with the bottle % of 6.

thx.

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