Today’s inquiry came to us from ‘Sally’, a new hot tub owner, who asked about the difference between free and total chlorine.

may sound dumb but I have just purchased a hot tub and these strips came with it, I
am not understanding the difference between total chlorine and free chlorine my test
shows 0 on both the rest of my colors are good what do I need to add? thanks

Believe it or not, Sally, we actually COMMEND you for having the courage to ask the question that you did… because too many people don’t ask questions and wind up with potentially unsafe water conditions!

For a tutorial on the differences between free and total chlorine we suggest you take a look at a popular blog entry on our site called “What is the Difference Between Total Residual Chlorine and Free Chlorine?“.

In a nutshell, however, if you use chlorine or bromine to sanitize your hot tub water then you have a problem that needs remedying right away: Your water contains no sanitizers — and you need to add some right away!

If, on the other hand, you use an alternative water sanitizing system (mineral ionization, ozone, peroxide, biguanide, etc.), then having no chlorine reading on either pad probably isn’t an issue.

Testing for alternative sanitizers

As more and more folks migrate towards alternative sanitizing systems for their spas and hot tubs, the need for testing methods for the alternative sanitizing methods grows.

Thankfully some methods, like the WaterWorks Peroxide Test Strips and the SenSafe Ozone Check, already exist.

Test Strips for Hydrogen Peroxide
Peroxide Test Strips

Test Strips for Ozone
Ozone Test Strips

And now for something completely (maybe) different…

Always consider the source water FIRST

Whether you have a swimming pool or a hot tub, the final quality of your water will depend heavily upon the quality of your source water (the water you fill your pool or hot tub with) and, more importantly, what you do to correct any issues that may exist with the water once you have added it to your pool or spa.

As ‘coders’ in the computer programming world often say, ‘Garbage In, Garbage Out!’

If your source water sucks, to use a term most of us definitely recognize, then without correction the water quality of any pool or spa filled with the source water will also suck.

Testing the water prior to the addition of chemicals makes total sense — unless, of course, you would rather spend money to fix problems like… staining on liners, fixtures, etc. caused by the addition of sanitizers (chlorine, bromine, etc.) which NEED to get added to the water.

Important Chemistry Lesson: Adding strong oxidizers like chlorine to water that contains dissolved metals like copper, iron, etc. may result in the formation of insoluble compounds that will settle on and stain any surfaces they encounter.

Visual Test Kit for Total Iron
Visual Test Kit for Total Iron

Test Strips for Copper
Test Strips for Copper

Water Metals Test Strips
Water Metals Test Strips

Spread the Water Testing Word!