The following is from a PM I received on another Pool Forum, but I thought the questions and answers were useful in general so I am posting this here with permission.
Hi Chem Geek,
You come highly recommended from a few people whom I work with, and I had a few questions regarding some pool water chemistry.
I work at a certain pool store down in FL, and I try my very best to educate customers (those who wish to put up with it anyway) when it comes to pool water chemistry. So getting to my questions:
1. We use a product called "stop green", it is not sodium bromide (which I think is mostly known as yellow out or yellow treat). I have searched my MSDS, looked on the internet and I can not find chemical make up of it. It is an ammonia based chemical and is supposed to work at higher PH's. Do you know anything about this chemical, and if you do could you explain to me how it works at higher PH's? I always thought that when the ph of pool water was around 7.8 or so, the hypochlorus acid broke down into the hypochlorite ion and hydrogen, which significantly reduces the oxidation effect of your bleach, so what doesn't make sense to me is how this works at high PH's. What I have always had very good success using sodium bromide at lower ph's. do you recommend one over the other?
2. I was thumbing through the forums and I found a good post about the differences between bicarb and just regular sodium carbonate.
I think I understand for the most part that bicarb raises your TA more than the PH, and sodium carbonate raises both PH and TA a decent amount. Can you explain to me as best you can what happens on a molecular level with these two? From what I understand PH is affected by the concentration of hydronium ions in the water? To me it would make sense that when the bicarb is dissolved in water the carbonates will affect the TA, sodium is just sodium, what does that extra hydrogen do? Does it not create more hydronium? Does it even break off of the carbonate ion?
3. I know CYA is a pretty touchy subject, and I am a strong believer in the 10% rule, which is keeping your FC 10% of your CYA. My question comes in the Trichlor- Tablets. There is a very big misconception in my specific area about Trichlor tablets, a lot of people "use" them as their main source of oxidation, this results in unGodly high stabilizer levels. One of the reasons that this misconception could be stemmed from is the way that our company advertises them, which is as "Chlorine Tablets". I know that the chemical break down of Trichlorisocyanuric acid is messy, but could you kind of break it down for me the best you can? I guess my question in specific is that they advertise 99% Available Chlorine in these things, how much hypchlorus acid do you get out of these vs actual CYA?
Thank you, and I look forward to hearing from you.