What Is The Hamilton Index For Pool And Hot Tub Water?

Written on:June 5, 2024
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What Is The Hamilton Index For Pool And Hot Tub Water?

Make adjusting your water chemistry a breeze using the Hamilton Index! And no, you don’t need any new chemicals either!

The Hamilton Index is a better way to adjust the chemicals in the water of swimming pools and hot tubs. It re-thinks all the “old ways” of testing and adjusting chemicals in order to give you better balanced water with much less cost and effort.

Here’s The History

In the mid 1990’s a California chemical research group was looking for a way to improve the chemical sanitization of swimming pools and hot tub spas. What they developed was named the Hamilton Index. It involves rethinking the ways people have always been taught to handle pool and hot tub water chemistry.

Most of the pool and hot tub industry uses what is called the “Langelier Saturation Index (LSI) for water balancing recommendations. The LSI was developed in the 1930’s for municipal water systems, and was required to be heavily modified to work for pools and spas. However it turns out that using LSI is not the best way to handle the water of pools and spas. The Hamilton Index was developed from the ground up to work specifically for the unique needs of pool and spa water.

The fact is that pools and spas have a fixed amount of water that is constantly being recirculated into the same water vessel – which is obviously not how public water systems operate. Also pools and spas are constantly being bombarded with a lot of external acidic contaminants such as rain water (acid rain with low pH), chlorine, bromine, shock, human sweat and other bodily contaminants, among others.

The Hamilton Index focuses on alleviating the effects of external acidic contaminants being added into the water. In short, the main benefits of balancing using the Hamilton Index versus other methods include: less adjusting required, less balancing chemicals, lower chlorine / bromine usage, less wall staining and scaling, longer structure surface life and more steady and predictable balancing.

Exactly How Does This Work?

Keep in mind that most of the “old” information about how to adjust pool and spa water chemistry has been handed down to pool and spa dealers by the manufacturers of the chemicals. This information was then taught to the pool and spa owners and has been passed around for years. But with the new information developed by the Hamilton Index, you can actually use less chemicals and have better sanitized water!

The basic concept is this. For many years, the accepted chemical level reading for chlorine / bromine was 2.0, pH was 7.4 and Alkalinity was 60-80. The Hamilton Index rethinks this accepted water chemistry. By analyzing the chemical reactions down to their molecular level, it actually turns out that these “old” accepted chemical levels are neither the most economical nor the best and easiest way to sanitize water.

Many pool and hot tub owners have had a lot of trouble maintaining their pH and Alkalinity at the proper levels. If they boost the Alkalinity level, the pH goes up too much. When they add pH Minus to bring down the pH, the Alkalinity drops way down. They are caught in a perpetual “Catch-22” and usually end up getting very frustrated! Proper use of the Hamilton Index specifically fights this problem of pH and Alkalinity “bounce” as well as cuts sanitizer use by up to 50%.

So what’s the best way to adjust the chemicals?

According to the Hamilton Index, the Total Alkalinity level should be kept much higher, at least 100-120 instead of floating between 60 and 80. Remember, Alkalinity is different than pH and must be tested with either a test strip or a 5 part dropper bottle test kit. The benefits of running a higher Alkalinity are: less sanitizer is needed, the pH is much more stable, there is a reduced tendency for cloudy water and stale smell, makes maintaining other chemical levels easier and reduces the possibility of corrosion to metal parts.

The pH level should be kept much higher, between 7.6 and 8.2 instead of 7.4 to 7.6. The darker red color on most test kits is better than the middle pink/red color. The benefits of running a higher pH are: less sanitizer is needed, sanitizer is more stable, less skin irritation, less chemical smell, reduces corrosion of metal parts, reduces chance of algae, improves water clarity, and higher pH is automatically “locked in” when Alkalinity is at 100-120.

Your sanitizer level (chlorine or bromine) should be much lower, 1.0 instead of 2.0. The lighter yellow color on most test kits is better than the middle yellow color. The benefits of this are: less sanitizer odor, less skin irritation, less inert chemical materials building up in the water, less water foaming, less sanitizer cost.

In conclusion, here are the main takeaways about using the Hamilton Index:

1- Alkalinity is the key component here.

2- You can raise water Alkalinity with any Alkalinity Plus chemical, which is basically sodium bicarbonate a/k/a baking soda!

3- You don’t have to play around with pH Plus chemicals that much. By keeping your Alkalinity higher, your pH will follow. This will make your water more resistant to those “pH bounce” problems.

4- With the pH and Alkalinity more “locked in”, your sanitizer (chlorine or bromine) will work more effectively and you will not need to add as much. It’s really that simple!

You will quickly find that maintaining your pool or spa water chemistry becomes much easier, and something that you only do once a week, rather than playing with it every few days. If you have any questions about using the Hamilton Index method for water chemistry, feel free to send us an email at

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