Hamilton vs. Langelier Index? What's Really The Difference?

[RobRM]

I've been poking around the internet and found the Hamilton Index. It talks about having a high pH, among other things. I think they also have their own line of products with United Chemicals. I found ChemGeek's post from 2008 but the information was a little sparse on the HI.

Really, what's the main difference between the two? Why would you use or not use it? I'm not talking about their line of bromide products, simply the actual Index itself.

Thanks in advance.

 

[JoyfulNoise]

Are you referring to this link - Hamilton vs. Langelier Index? What's Really The Difference? ?

First of all, they get a few things quite wrong. They dedicate three paragraphs to try to "prove" that high pH is a good thing because it makes your sanitizer work better. That is completely false when it comes to a residential outdoor pool that uses stabilizer (CYA). Once even a minimal amount of CYA is present in pool water, most of chlorine is bound by the CYA and held in reserve and only a much smaller fraction is left as active chlorine, i.e., hypochlorous acid (HOCl) and hypochlorite anion (OCl-). At a pH of 7.5, the ratio of HOCl/OCl- is roughly 1:1. As your pH increases you get more hypochlorite anion (OCl-). However, for sanitation purposes and oxidizing of bather waste, hypochlorous acid (HOCl) is what you really want. HOCl is a much more potent sanitizer than OCl- and a far better oxidizer of bather waste and other organic molecules. As well, the hypochlorite anion is the component of active chlorine that is much more susceptible to UV photolysis and it is the reason why your pool loses FC all day long. So you actually want LESS OCl- not more. So their "sanitizer is better at high pH" argument is totally bogus and does not apply at all to residential pools.

The Hamilton Index also uses total hardness (TH) as it's primary control. TH is not measured in pools as calcium hardness (CH) is much more important for pool water. TH typically measures both the calcium (Ca²⁺) AND magnesium (Mg²⁺) cations (none of the other Group 2 alkaline earth metals are typically present in pool water). They make the claim the metal carbonates are very insoluble and that is correct....except in the case of magnesium carbonate which is ~ 10X more soluble in water than calcium carbonate. Magnesium scale is almost NEVER an issue in pool water so there is no point in measuring it.

TFP advocates the use of the Calcite Saturation Index (CSI) which is a variation of the Langlier Saturation Index that takes into account all relevant parameters of pool water (pH, CH, TA, temperature, salt, etc) and yields a value which is the logarithm of the relative saturation value of pool water for calcium carbonate. The calculations are all performed in Pool Math so the user does not need to use complicated look-up tables.

Finally, if you look at what they say on that website as "Recommended" ranges, some of that is impossible for anyone with a plaster pool or a pool located in arid parts of the country. They are correct that pH isn't the most critical parameter, but neither the LSI nor the CSI are based SOLEY on pH.

And, just to add a bit of cynicism, they are probably pushing their index to get people to login in to their website in order to increase their marketing penetration...if their Hamilton Index is so great and wonderful, then why is it behind a login wall? TFP offers Pool Math for free on the internet (in fact, that's how I "accidentally" found TFP....)

Matt

 

[RobRM]

Thanks. I've often wondered why they want the pH between 7.8 - 8.2. My understanding is the FC is less active as the pH increases, but you need to throw the CYA into the equation as well. The TH, in my understanding, is very hard to correctly measure. I lived in Mesa and the hardness of the water was 300ppm. According to them that's too high, but what should a pool owner do? Not have a pool? I take care of a neighbors pool and basically use the same parameters set forth here. Her CYA was 100ppm so I did a partial drain and refill, balanced everything using liquid chlorine, and kept the filter cleaned out. 17K gallon pool with moderate Summer use costs about $20 per month in chemicals. Not bad. I also know that the HI and United Chemicals uses No Mor Problems which is bromide based. They say keep your readings at our levels (FC at 1.0ppm) which is waaaaay to low for hotter places like AZ and FL. I'm 1ppm away from bottoming out. Then they come back and say supplement the lower FC level with the aforementioned product? I keep an eye on the CYA. Everything else is simple to adjust.

 

[JoyfulNoise]

Bromine based algaecides and sanitizers make pools anything but trouble free. The excess bromine in the water will act as a source of constant chlorine demand because bromide gets oxidized by chlorine to form bromine. Bromine acts as an effective sanitizer and algaestat (especially against harder to kill algae like black algae), but it will constantly use up a pools chlorine reserve. As well, there's no way to differentiate between chlorine and bromine with halogen tests so it becomes exceedingly difficult to figure out exactly what your chlorine levels are.

Best to stay away from bromine products in swimming pools.