Need 2nd Opinion on % vs Volume vs $ calculation/assumptuion

[Sponge1971]

Hi Eh!

Up here (in the Great White North) Walmart doesn't have an Ultra Wally brand. (there is an Ultra Javex jug, but it's only 5% and $4?..can't remember since I'm not interested)

Walmart only sells a $2 - 5liter jug of 4% bleach (which is great, I guess, and pounds the ppm's into the stratoshere when you dump 4 jugs in during your initial fill...because you don't know any better......boy, you should have seem the crazy neon pink in my testkit when I checked for FC...)

Anyway, here's my question:

I need to confirm my math on what is best the value for money between these two options:

1. Walmart - 5liters @ 4% = $2
2. PoolStore - 20liters @ 12% = $11

Here is what I think is true...but I need a fresh mind(s) to confirm:
- If I want 12% equivalence, from 4%...I need 3x more volume. So, 3liters of 4% is equivalent to 1liter of 12%. <- this is the cornerstone of my assumptions...

- based on the above assumption: to come up with the same 'punch' that 20liters @ 12% = $11 has...I would need 60liters @ 4% = 12 jugs = $24 total.

- It is far more cost effective for me to go with the PoolStore 12% jug. (even after the 1time $15 jug purchase).

Let me know what yous think...

[aylad]

It is more cost effective to go that route....IF it's actually 12% or more in strength. Depending on storage conditions and turnover rate, the 12% may or may not degrade. I'll have to find the link for it, but around here somewhere Carl (or maybe Waterbear?) concocted a way to test the percentage of chlorine actually in the jug. Let me search around some and see if I can find it, and will add it here.

Edit: Here it is... http://www.poolforum.com/pf2/archive...p/t-10167.html

[Sponge1971]

thanks! I'll go look at this and let you know what my jug is at...

I was thinking about shelf life. It is 'possible' that the Walmart jugs are way fresher...unless they warehouse for a year...but they still would be in a dark climate controlled box...if that makes any difference

[aylad]

But the difference is that lower concentrations of chlorine degrade slower than higher concentrations. I can't explain the chemistry behind it, but chem geek, pooldoc and a few others around here can. So even if the WalMart stock is not as fresh, it may well hold its concentration better than the 12%.

Janet

[giroup01]

You need to compare the quantity needed for 1 ppm in a 10 000 liter pool, you can take it from there.

The WalMart stuff, you need 250 mL of 4%, cost per ppm, $0,10
The pool store stuff, you need 83 mL of 12%, cost per ppm $0,05.

If you think of "cost per ppm" then it becomes very easy to determine if the price is good or bad or average.

Walmart probably has higher turnaround than the pool store, you could ask the pool store to check the actual chlorine content of the 12% stock (only 0,5 mL is needed if you use the Taylor bleach kit).

12% degrades much faster than the 4% stuff.

Bleach isn't necessarily cheaper by the way, Trévi has (had) cal hypo, 14 kg of 65% for $38, you need 15 grams for 1 ppm, cost per ppm $0,04.

I keep all that info in a spreadsheet, the Walmart bleach is actually one of the more expensive solutions to date, Trévi being the least expensive.

[CarlD]

1 milliliter of 12% added to 10 liters of water is the same ratio as adding 1 liter of 12% to 10,000 liters. (I usually do it in gallons but the ratios are exactly the same).
So test your tap water and get a baseline FC reading.
Then put 10 liters of tap water in a bucket (since even in the US 2-liter soda bottles are everywhere, 5 of those works).
I use a drug-store eyedropper (glass, of course) with measures on it already for 0.5 and 1.0 ml. Add 1ml of 12% to the 10 liters and mix it up. Let it sit for 10 or 15 minutes.
Measure with your K-2006 FAS-DPD test to find the chlorine level, and subtract the FC of the tap water.
The resulting measure is the actual concentration of your liquid chlorine.

(This comes from the formula for ppm: Parts per Million.
((1,000,000liters/10,000liters [pool volume]) * .12 * #liters of chlorine) = ppm, where .12 is 12% strength liquid chlorine. You can substitute .0525, .06, .105, or .125, depending on the claimed concentration. # Liters is assumed to be 1, but can be more. Again, it works just as well if you substitute gallons for liters everywhere. I simply reduced it from 1,000,000 liters to 1,000,000 milliliters, pool volume to 10,000ml and # Liters, becomes #ml.)

Carl

[Sponge1971]

Excellent Guidance!

My tap = 1.2ppm (did the high precision 0.2/drop measure)
My 10l & 1ml sample (blended and 10mins) = 11.5ppm (0.5/drop)

Bleach concentration = 11.5-1.2 = 10.3ppm = 10.3%

I guess that's not too bad. I never realised the conc could drop so much. I'll have to check again in a month, just to see the rate. There could/will be a point where other options would be more cost effective...depending on my consumption.

thanks Carl!

[CarlD]

Glad to help!

The higher the concentration the faster it can break down. Apparently, the solid blue carboys LC is sold in here in my area is really good at protecting the stuff.

Carl

[giroup01]

On the bleach bottle you read the % concentration of sodium hypochlorite.
What you are measuring is the concentration available chlorine content.

Not the same thing.

[CarlD]

On the bleach bottle you read the % concentration of sodium hypochlorite.
What you are measuring is the concentration available chlorine content.

Not the same thing.

What is the point of that?

The whole point of the calculation is to determine how much available chlorine the Bleach/Liquid Chlorine will deliver. Ultimately, that's what you need to sanitize your pool, and the concentration is merely a guide to get you there.

Parts Per Million added = (1,000,000 / pool volume) * (Bleach or LC Concentration (as a decimal)) * (amount of bleach or LC used)

If you add 1 ml of bleach or LC to 10 liters of water the resultant Parts Per Million measured, less the public water's residual FC is = to the concentration of the bleach bottle.

What's the problem?

Carl