Sunday, December 24, 2006
WE WISH YOU A MERRY CHIRSTMAS AND A HAPPY NEW YEAR
I'm taking the weekend off from the blog to celebrate. But I have been busy this week. I found a new forum, called the Garden Web. I posted a few comments there and the Salt System Cheerleading Squad called me names and threw sticks at me and told me my mother dresses me funny. In my usual polite and affable way, I wished them all the best with their pool degenerators.
But I did meet two very interesting folks while there. The first is a fellow from Australia named David. He has a pool forum that he's just getting off the ground. I hope everybody will take some time out and go visit his forum and take some time to post your questions and comments there. I have been chatting with him via e-mail about the differences between the US and Australian salt system markets and my next post to the blog will be a very illuminating explanation of why it works so well there and not so well here. I couldn't have done this without David's help and I hope all of you who read this blog on any kind of regular basis will return his courtesy to us and visit his forum and help him make it a success.
Find his forum at: http://poolindustrysecrets.aceboard.com/
If you don't visit it now, I know you will after you read the next blog piece about what he has to say about his market and about ours. This is a fellow you are going to want to know. Especially when the Reps start feeding you their BS about how "this is exactly the way they do it in Australia". You'll be able to call BS. Not to mention the phenomena's related to salt that he's talking to me about that we're struggling with every day and they just take for granted and work around Down Under because they've been doing it for so long.
The other fellow I met goes by the screen name Chem Geek. He's made several comments on the piece I did back in October, titled Why Salt Sucks. Read his comments and my answers by going here:
He mainly posts at the Pool Forum. He has even started a thread about our little blog here. You can access it by going here:
Even though he's just a pool owner, and even though he had the nerve to refer to me as "just a pool cleanup guy who doesn't know science", I like him, and if I get the chance to meet him some day, I probably won't kick his ass. You know, being a knuckle dragging pool cleanup guy, that's the first thing that crossed my mind. But I'm trying to be big about it and let the Christmas spirit fill my heart with forgiveness. Besides, he's wicked smart and I think he's going to be able to answer a lot of our questions about the problems we're seeing with salt systems. And if you have any questions about just how wicked smart this guy is, I'm going to reprint his explanation of why we ought to run lower TA's on salt pools and why we see a rise in pH with salt systems instead of the pH neutral horse manure story the Reps give us. Here is his explanation in italics.
I just wanted to correct what you said technically because what you said was not exactly true and I don't want the main point of running with lower TA helping to reduce the pH rise get lost because of technical inaccuracies. The salt cell has the following two primary reactions:
2Cl- --> Cl2(g) + 2e-
2H+ + 2e- --> H2(g)
2H+ + 2Cl- --> Cl2(g) + H2(g)
The chlorine gas almost immediately dissolves in the water with the following reaction to have a net reaction as shown:
Cl2(g) + H2O --> HOCl + H+ + Cl-
H+ + Cl- + H2O --> HOCl + H2(g)
Because water dissociates, the above reaction is normally written with a net reaction as follows:
H2O --> H+ + OH-
2H2O + Cl- --> HOCl + OH- + H2(g)
So the bottom line net reaction with the generation of chlorine in a salt cell (ignoring side reactions) is that water and chloride ion (from salt) combine to form hypochlorous acid (HOCl) plus hydroxyl ion (which is basic or alkaline) and hydrogen gas. Since hypochlorous acid is a weak acid, this net reaction is weakly basic (alkaline). This is where most SWG manufacturers (at least their salespeople) believe that the rise in pH comes from, but they are wrong (keep reading to find out why).
This is pretty much exactly the same thing that happens when you add chlorinating liquid or bleach to a pool as follows:
NaOCl --> Na+ + OCl-
OCl- + H+ --> HOCl
H2O --> H+ + OH-
NaOCl --> Na+ + HOCl + OH-
except that you get some sodium ion as well (plus some extra salt, NaCl, that is in sodium hypochlorite solutions due to how they are made) and you don't get the hydrogen gas.
Now we need to look at what happens to chlorine (regardless of source) when it gets used up. Most chlorine in pools gets broken down by sunlight and even though Cyanuric Acid (CYA) combines with chlorine to form a chemical compound that slows down this process (and is not an effective disinfectant or oxidizer), it still happens as follows:
2HOCl --> O2(g) + 2H+ + 2Cl-
The next most common thing that happens to chlorine is that it combines with ammonia or related compounds such as urea from sweat as follows where I show the reaction going all the way to "breakpoint" assuming that shocking occurs (which it usually does if you have sufficient chlorine in your pool and especially when exposed to sunlight which helps the breakpoint process). I'm not going to show what happens when chlorine combines with organics, but the process is somewhat similar (carbon dioxide is produced if the organic is fully oxidized, but more typically intermediate compounds are produced that don't breakdown quickly).
2NH3 + 3HOCl --> N2(g) + 3H+ + 3Cl- + 3H2O
So, even though the generation of chlorine resulted in hydroxyl ions, the usage of chlorine results in hydrogen ions and these cancel out forming water:
OH- + H+ --> H2O
So the bottom line in an SWG pool is the following reactions:
4H2O + 2Cl- --> 2HOCl + 2OH- + 2H2(g)
2HOCl --> O2(g) + 2H+ + 2Cl-
2H2O --> 2H2(g) + O2(g)
6H2O + 3Cl- --> 3HOCl + 3OH- + 3H2(g)
2NH3 + 3HOCl --> N2(g) + 3H+ + 3Cl- + 3H2O
2NH3 --> 3H2(g) + N2(g)
So the bottom, bottom line is that the net result in an SWG pool from the creation and usage of chlorine is that water is split to produce hydrogen gas and oxygen gas or that ammonia (urea) in the water is broken down (oxidized or "burned" in some sense) to produce hydrogen gas and nitrogen gas. These net, net reactions, as you can see, are neutral.
At this point, you can now talk about the source of rising pH being the outgassing of carbon dioxide from the pool. You should explain that pools are in essence intentionally over-carbonated, similar to a lovely tasty carbonated beverage! This is done when you initially added baking soda or sodium bicarbonate to your pool (it also happens when you add some pH Up products that have sodium carbonate). The purpose of having extra carbonate in your pool is to act as a pH buffer and to provide carbonate ion that, along with the calcium you added to your pool with calcium chloride, saturate the water with calcium carbonate so that this compound does not get dissolved out of plaster/gunite/concrete/grout. If too saturated, scaling would occur essentially precipitating calcium carbonate on to pool surfaces. Also, the calcium carbonate tends to form a thin film layer on metal surfaces that help reduce corrosion, though pH is a much more important factor for metal corrosion. Pool water chemical balance attempts to keep a balance between corrosion and scaling.
The downside of having a pool over-carbonated is that there is more carbon dioxide in the pool than in the air so there is a tendency for it to outgas. When this occurs, the pH rises while for technical reasons I won't get into here, the Total Alkalinity (TA) remains the same. If you then add acid to restore the pH, you lower both the pH and the TA with the net result of having TA get lowered -- which makes sense since TA is partly a measure of the amount of bicarbonate in your pool. The carbon dioxide outgassing, and therefore the rise in pH, is increased when the TA is higher, when the starting pH is lower, and when there is more aeration. So the easiest ways of reducing this rise in pH are to lower the TA, keep the pH higher, and reduce aeration (waterfalls, spillovers, etc.) including using a pool cover.
For an SWG pool there is another way, in addition to lowering TA, that can help reduce the pH rise. That is to add an additional buffering system to the pool that is also an algicide that will cut down chlorine consumption. Adding 50 ppm Borates (from Borax, the 50 ppm technically being Boron) to your pool will add additional pH buffering capability so that you can keep the carbonate part of the buffer lower. To compensate for water balance, you need to keep either your calcium level or your pH higher (or both). The algicidal properties of the borates lower the consumption of chlorine which will let you lower the output of your SWG which lowers hydrogen gas production so less aeration so less carbon dioxide outgassing and less pH rise. Whew!
I told ya. Ain't he wicked smart?
All joking aside, I really appreciate the Chem Geek's contributions to this blog and I appreciate his posts over at the Garden Web and especially the Pool Forum.
Meeting these two fellows has made me feel very optimistic that in the weeks to come, we'll be able to put out some truly pertinent and highly accurate information about these salt systems.
Labels: Pool Forums