I experimented with CO2 injection in the late 80's -- even built my own injection system using German fused glass bubblers. The problem I found is that when you use CO2 to control pH, you get uncontrolled carbonate (-HCO3 + =CO3) build up. This is a result of using CO2 to form carbonic acid (H2CO3) which, as it lowers pH, is 'converted' to carbonates.

In general, I found it to be inefficient and troublesome, compared to muriatic acid. Shortly after that, I discovered how to keep muriatic acid from fuming, and I no longer had any reason to mess with CO2. I've since seen it used on a 700,000 pool (not a pool I was servicing) in conjunction with a Strantrol ORP/pH controller, at huge expense and constant problems.

Ben

PS. My very strong impression is that Hayward's new focus on technology and the commercial pool market is almost totally marketing driven, rather than engineering driven. This does not inevitably produce flashy, but sucky products (a la Zodiac) but that's certainly the tendency.