Although both manufactured by Industrial Test Systems, Inc., a US based company in South Carolina, the DPD-1 ReagentStrip and SenSafe Free Chlorine Water Check products test for free chlorine residual in very different ways.

The chart below will explain the differences and similarities between the two free chlorine residual test methods:

	DPD-1 ReagentStrips™	SenSafe™ Free Chlorine Water Check
Detects:	Free Chlorine Residual (and Other Oxidizers Normally Tested Using DPD-1 Chemistry)	Free Chlorine Residual
Test Procedure Overview:	Liberarting of DPD-1 Reagents Off Reagent Pads Into 10mL Sample and Checking Chlorine Concentration Visually by Color Comparator or Electronically Using a Colorimeter	Immersion of Test Strip in Water Sample, Removal of Test Strip After Specified Period of Time, and Visual Comparison of Developed Color in Test Area to a Color Chart
Detection Range:	0-6ppm	0-6ppm
Accuracy & Precision:	Depends on the Method Used to Interpret the Developed Color in the 10mL Sample. Visual Methods Will Have Less Precision Than Meters	0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.2, 1.5, 2, 2.6, 4, 6 ppm (mg/L)
Certifications & Compliance:	DPD Testing as Specified in 4500-CL G Check w/ Your Local Health Department for Final Word on Compliance	USEPA Approved Test Method for Free Chlorine Read the EPA Letter   View EPA Approved methods   Check w/ Your Local Health Department for Final Word on Compliance
Number of Tests:	100 Tests per Package	50 Tests per Package
Benefits:	Cleaner to Use Than DPD-1 Powders (i.e. DPD-1 Powder Pillows)   Dissolves Easier Than DPD-1 Tablets   Longer Shelf-Life Than DPD Liquid Reagents   No Undissolved Solids When Testing in Cold Water (5ºC)   Requires No MSDS	Safe for Use on Most Production Floors   Requires No Specialized Testing Knowledge   No Expensive Meter (Colorimeter)   Designed to Resist Monochloramine Interference   Requires No MSDS
Per Unit Cost:	$15.99 per Package of 100 Tests	$15.99 per Bottle of 50 Tests

As always, if monitoring free chlorine residual for reporting and/or compliance monitoring we suggest contacting your local health inspector before switching to a different chlorine testing method.

Although seemingly counter-intuitive, many methods approved on a Federal level may not have attained acceptance, yet, on a State or Local level.

In the water business testing for free chlorine happens quite frequently (as Scott just said)… and we know of two ways to make that task easier:

• DPD ReagentStrips — If you use DPD-1 to test for free chlorine residual, then undoubtedly you do so using DPD in powder or tablet form. Both methods work, but DPD-1 ReagentStrips make testing for free chlorine residual in water a faster and easier process while staying in compliance with 4500-CL G. Simply insert a DPD-1 ReagentStrip into a 10mL water sample, move it back and forth (liberated required DPD chemistry off of reagent pads), and read visually or with your favorite meter.
   
• SenSafe™ Free Chlorine Water Check — In the original recommendation letter from the USEPA, dated October 2003: “We believe that the ITS test strips will provide the regulatory community with a valuable option for monitoring free chlorine levels in drinking water.” This method bears USEPA Approval for in drinking water applications.

While both testing methods make free chlorine residual testing much easier without losing accuracy, we highly suggest check with your State and Local inspectors first before using either product for compliance monitoring… because as you know (probably better than we do!), sometimes State/Local regulation changes do not always keep up with Federal Regulation changes.

Not sure of the differences between the different DPD numbers? No worries! A while back we posted a pretty good article called What is DPD? that should answer the majority of your questions.

Getting back on topic, though, we have started carrying DPD # 1 Test Tablets and DPD # 3 Test Tablets in the DPD Test Reagent section of our Pool Water Test Kit Store. At this time we carry the Pentair brand.

Additionally, on this site we carry the DPD #1, #3 and #4 ReagentStrips in our Water Test Kit Store.

At this time we carry 100 packs of DPD-1, DPD-3 and DPD-4 in the Water Testing Blog Test Kit Store.

Differences between DPD-1, 3 and 4?

For the answer to that question, we suggest that you take a look back at one of our earlier postings called What is DPD?. Not to brag, but we think that article does a decent job of answering the question.

To sum things up, though, below you will find the most common uses for DPD-1, DPD-3 and DPD-4:

• DPD-1 — Used by itself in a water sample to determine the free chlorine concentration in the sample.

• DPD-3 — Used after DPD-1 in a water sample to determine the sample’s total chlorine concentration.

• DPD-4 — Used by itself in a water sample to determine the total chlorine concentration in the sample.

So, before purchasing DPD, you may want to verify the type of chlorine testing that you will need to do — else run the risk of accidentally purchasing the incorrect DPD reagent(s)!

Where to purchase DPD?

As we stated earlier, you can purchase 100-packs of DPD-1, DPD-3 and DPD-4 from our Water Test Kit Store.

As for where to find other forms of DPD reagents, at this time we know of places to purchase two other forms of DPD: tablets and powder.

Need a new meter to test chlorine levels, too? We suggest looking at the eXact Chlorine Photometer available on the FilterWater.Com web site. It offers the reliability of DPD-based chlorine testing and the convenience of not having to match colors against a color chart.

Want accurate chlorine test results but don’t want to deal with DPD reagents and meters? Take a look at the SenSafe Free Chlorine water Check product currently available in our Water Test Kit Store. It bears USEPA Approval for use in municipal water testing and offers superior resistance to monochloramine interference that can sometimes affect the results obtained when testing for free chlorine residual using DPD test reagents.

Today’s inquiry deals with DPD for free chlorine testing and came to us from ‘Oviruo’ who asked, “please can you assit me to get dpd satchet powdered type for testing free chlorine in water. thanks.”

We did a quick check and found that you can purchase DPD-1 Powder Pillows for Free Chlorine Testing on the Hach Company web site. The material has an approximate cost of around $21 per 100 powder pillows.

Alternative to powder pillows

A company called Industrial Test Systems came out with an alternative to the powder pillow that performs as well or better than the powder pillow. They called it the ReagentStrip and it works quite well without the mess that sometimes accompanies the act of trying to pour a small packet of DPD powder into a sample vial.

Below you will see how the DPD-1 ReagentStrip works when used with the Hach 890 Water Testing Meter:

Free Chlorine Testing Using DPD-1 ReagentStrip
and Hach’s 890 Water Testing Meter
click on image to view larger version

According to the manufacturer, DPD-1 ReagentStrips work with chlorine testing meters manufactured by well-respected companies such as Hach®, LaMotte®, Orion®, WTW®, and others.

Additionally, the DPD-1 free chlorine testing procedure stands and an equivalent to USEPA method 330.5 for wastewater and Standard Method 4500-Cl G for drinking water when used with a Palintest Chlorometer 1000 water testing meter or equivalent.

Cost of DPD-1 ReagentStrips compared to powder pillows

Earlier in this article we mentioned that interested parties can pick up 100 DPD-1 powder pillows for around $21 on Hach’s web site.

For those interested in the DPD-1 ReagentStrips, you can purchase 100 of those for around $19 on FilterWater.Com.

Dear Sir

Please could you quote a best price for: Chorine- DPD Free Reagent Qty:600 Pk, each pk containing 100 pillows

When testing for free chlorine most test methods use DPD-1 as the test reagent, though in the United States the USEPA has approved an alternate method (SenSafe Free Chlorine Water Check) for testing free chlorine levels in drinking water.

Where to Buy DPD-1 Test Reagents

We have found that online pool stores such as serve as very convenient place to purchase DPD-1 test reagents. As of right now, In the Swim has 1,000 DPD-1 tablets (for use in 10mL samples) available for less than 5 cents per test!

Easier to Use Form of DPD-1 Chlorine Test Reagent?

Looking for an equivalent but easier way to test free chlorine using your existing meter or test system that uses a 10mL sample size? If so, DPD-1 ReagentStrips function the same as or better than traditional DPD-1 test tablets, powders and liquids.

For a simple demonstration of how the DPD-1 ReagentStrips for free chlorine testing work in a Hach water quality testing meter, take a look at this free chlorine testing flowchart that illustrates how much easier DPD-1 ReagenetStrips make free chlorine testing.

1,000 DPD #1 Tablets

Recently we received a request for a quote on 5,000 DPD #1 Tablets for chlorine (or possibly another oxidizer) level testing. We’d like to remind remind everyone that although we link to a number of water quality products, Water Testing Blog does not stock or sell any products.

The party asking about DPD #1 Tablets sought to import them into a foreign country so we suggested they contact companies on the following page:

( http://www.alibaba.com/showroom/dpd-tablets.html )

… so they could attempt to save a few bucks (or whatever currency they use) on shipping.

Now having said that, when it comes to DPD #1 we believe anyone thinking about using DPD tablets should at least consider using DPD-1 ReagentStrips in their place. ReagentStrips dissolve faster and easier than tablets (especially in hard or cold water) and contain no filler materials that could interfere with photometric optics.

As far as performance, the manufacturer of DPD-1 ReagentStrips, Industrial Test Systems, Inc., had an independent laboratory conduct a blind water sampling study using DPD ReagentStrips, Tablets and Powder Pillows. In the end the ReagentStrips tested as good, and in some cases better, than other DPD reagent delivery methods.

The US Environmental Protection Agency has set the Maximum Contaminant Level (MCL) for free chlorine at 4.0 parts per million, also known as milligrams per liter (mg/L).

The most commonly used test for free chlorine residual uses a reagent called DPD (what is DPD?). More specifically, it requires DPD-1 and DPD-1 comes in several different forms: liquid, powder, tablet and reagentstrip form.

With that in mind, please excuse our departure from the normal subject matter and indulge us as we answer a question about purchasing DPD test tablets for chlorine testing in Zambia, an African Nation.

“Robert K” asked…

I need to know if there is company in Zambia or Sub-sahara Africa selling DPD #1 tablets.

This is a very informative site, keep it up

Thank you, Robert, for contacting Water Testing Blog with this question. We don’t know a whole lot about companies doing business with other areas of the world such as Zambia, but we did find a few links that may prove useful information.

• http://www.wisa.org.za/Home/Home.htm — Water Institute of Southern Africa
• http://www.smianalytical.co.za/water-analysis.html— SMI Analytical Services Provides Water Testing Services to South Africa
• http://www.merck-chemicals.co.za/contact — Contact Merck Chemicals (Zambia Office)

• http://www.mobilis.co.za/ — Imports Pool Chemicals & Testing Supplies Into Africa

Sorry we cannot provide more assistance than we have, but we do hope one of the links above will point you in a useful direction.

For those interested in learning more about DPD and its uses, please check out an earlier posting entitled What is DPD?.

If you would like to purchase DPD from a retailer/distributor in the US, the following links will take you to a site where you can order DPD #1 and/or DPD #3 in packs of 100 and packs of 1,000.