Chlorine Test Strips

How to Dilute Chlorine Bleach? It’s Easy!

Chlorine Sanitizer/Disinfectant

Chlorine bleach is an inexpensive and widely used chemical for sanitizing and disinfecting in restaurants, childcare centers and hospitals. The recommended concentrations for use in them varies from 200 to 10000ppm.  Labels on supermarket bottle of bleach products offer little guidance on how to dilute bleach correctly for most of these uses.

What is ppm & Why Use It?

You encounter dilutions/concentrations on a daily basis in many common things. Most liquors are 40% (80 proof) ethanol  with the rest mainly water. 1 or 2% milk refers to the amount of fat with the rest being mainly water with some protein and sugar (lactose).

PPM (ppm) or parts per million is used mainly when very small amounts of one thing are part of a larger thing. Consider money as an example. A cent (penny) is 1% or 1/100th of a dollar which could also be expressed 10000 ppm. A more practical description might be one penny in $10,000 is 0.0001%  or 1 millionth which is the same as 1ppm.

Note that a very common usage in science of this is weight/volume, shown as mg/L. This describes the weight of something dissolved in a liquid and can also be expressed as pp.

Chlorine bleach test strips
Chlorine test strips cover a variety of ranges. The leftmost is for residual levels of 0-10ppm. In front are  200ppm restaurant strips and behind them the very high level 10000ppm. To the right are the 2000ppm which are popular in childcare centres.

Chlorine Bleach Labels-USA

Below is a label from a typical brand of chlorine bleach. The dilution instructions are relatively easy to follow but the bleach strength isn’t indicated anywhere so you can’t tell what ppm you get even if you follow the instructions perfectly.

If we assume 5.25% and dilute according to the sanitizing work surfaces instructions, 1 tbsp in a gallon, we get about 200ppm. This is a common concentration especially in restaurants but is lower than what is used in daycare or hospitals.

US Chlorine Bleach Label
Information for meeting the sanitizing & disinfecting regulations used in different cities, counties & states is missing from this label.

Diluting Chlorine in American Units

You can work out any dilution with our Dilution Calculator but since it uses metric units, use these as a guide:

1 tsp=5ml
1 tbsp=15ml
1 cup=~235ml (or round to 250ml)
1 quart=~950ml (or round to 1000ml/1L)
1 Gallon=~3800ml (or round to 4000ml/4L)

Now you try it.  (steps 1,2,3,4 refer to where you enter numbers in the calculator) :

  1. Enter 5.25% for the concentration (step 1).
  2. Then 200ppm for step (2).
  3. Then 3800ml for step (3)
  4. Press Calculate.

You’ll see a result in the box for step (4) that says 14.48ml which is very close to 1 tbsp.

You can work backwards. Clear the 200ppm from step (2), enter 15ml in step (4) & press Calculate. You’ll see 207ppm appear in the box for step (2). This is close to 200ppm.

The label instructions for disinfection call for 3/4 cup in 1 gallon. If you work this out in the Dilution Calculator, you get about 2500ppm.  Since many state regulations call for only 500, 800, 1000 or 2000ppm, you end up using far more bleach than you need. 1

If all you need is a spray bottle to sanitize faucets, handrails or countertops, a gallon is too much.  To make up a quart  diluted to 1000ppm,  just enter the following steps in the  Dilution Calculator:

  1. 1.5.25% for step (1)
  2. 1000ppm for step (2)
  3. 950ml for step (3)

Pressing Calculate gets a result of 18.1ml which you can round up to 20ml or 4tsp.

Chlorine Bleach Labels-Canada

The Canadian label has instructions in metric units that are of little use.  Dual unit measuring cups have metric units on one side. The markings goes to 125ml & 250ml, not 120 & 240ml. Larger 4 cup versions have metric markings at 500 and 1000ml (1 litre) not 475 & 950ml.  What to do?

Canadian Chlorine Bleach Label
These instructions say 120 & 240 ml instead of the 125 & 250ml that are the actual graduations on the metric side of a measuring cup.

Since percentage and ppm are based on units of 10, preparing a 1 litre (1000ml) spray bottle for 200ppm is simple. Just enter the following in the Sanitizer Dilution Calculator:

  1. 5.25% for step (1)
  2. 200ppm for step (2)
  3. 1000ml for step (3)

Press Calculate and you get 18.1ml which rounds up to 20ml or 4tsp.  This works out to about 1100ppm which is within acceptable limits.

What PPM is Too High or Too Low?

The human eye can detect over 10 million colors but subtle shade differences are still hard to see.  2  Our eyes evolved to see color using natural sunlight but indoor lighting such as fluorescent, halogen or LED can make things look more yellow or blue or somewhere in between. 3  As long as the color chart matches what you want pretty closely, you’re ok.

Your health inspector likely prefers a dilution on the the high side. A bleach solution that is a little low will still work but take a little longer to kill germs. Besides, that is why there are test strips to let you know you are within range. .

References

  1. Different bleach test strips: 200ppm; 1000ppm; 2000ppm; 10000ppm
  2. Find out more about Color Vision & what we can see?
  3. Light and how it affects the colors we see is a complex topic. It is best to start with understanding Full Spectrum Light, i.e. sunlight.

Test strips of 0-200ppm are commonly used in restaurant kitchens. (see our blog: Wash/RInse/Sanitize) . Cruise ships and senior’s homes often use 1000ppm levels. Some daycare centers prefer the 2000ppm test strips which can indicate accepted sanitize & disinfect levels such of 500 & 800ppm.  Health care facilities such as hospitals are the main users of the 10000ppm test strips since these allow for chlorine uptake by organics  such as blood.

If you aren’t sure what you need, contact your local health authority. If you need assistance buying strips, give us a ring at (877)746-4764 betwen 8:30-5:00 Eastern Time, M-F.

About Stephan Logan

VP Sales & Marketing at Indigo Instruments. Previously sold hi tech science instruments to researchers. B.Sc. & M.Sc. from McGill University.

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