Evan (waterbear) also makes good points. If we really want to get to the bottom of this, we would need ALL of the relevant pool water chemistry information that all of you in these forums know is what is asked of you when you want people to help you with your water problems. Of particular relevance for this SWG algae discussion would be minimum FC level, CYA, and pH. The TDS is already roughly known and not a big factor nor is the CH or alkalinity (except that very low alkalinity can lead to large pH swings you might not be aware of) -- I'm not talking about water balance to protect plaster, but rather those components that affect disinfecting chlorine concentration.

Anyway, I don't want to bash SWG systems in any way. Even though I don't have one, I think they are great and the most important service they provide is that they automatically maintain FC levels. And then there's that silky feel of salt water...oooooooo, you've got me thinking about getting an SWG myself!