Downsides to salt pools

[chem geek]

Richard, your explanations of SWG chemistry are truly awesome, but I don't believe for NY second that the reason for the manufacturers' 70-80ppm CYA recommendation (I've actually seen 80-100ppm recommended) has anything to do with real-world chemistry. Rather, I suspect it has more to do with a slightly different interpretation of the acronym "CYA", rooted in the early days of the SWG evolution when reliable operation was not up to par with current devices. In a loss-of-power event, for example, high CYA levels would help to ensure that all your residual FC doesn't disappear on a sunny day before you've noticed something is amiss. I believe there is no longer any rationale justification for this recommendation other than my suspicion that the manufacturers have no interest in pursuing the matter and are content to leave it unchanged.
Personally, I barely manage to keep my CYA level above 25ppm, and have experienced no consequences from that during the four seasons I have operated my Pool Pilot SWG -- although I do test my FC and Ph quite often.

I want to apologize to you (and others) for very likely being wrong about the higher CYA improving SWG cell efficiency. The experiments Mark describes in the later posts in this thread have pretty much confirmed that SWG efficiency is not affected by CYA level (at least not from 45 to 80). There is some effect on efficiency from pH.

I incorrectly assumed that the industry charts showing the half-life of chlorine vs. CYA level were correct and based on experiments, but apparently they are wrong and based on incorrect assumptions or too few data points. Mark's tests plus feedback from other users shows that higher CYA levels protect chlorine by more than accounted for by simply forming more stable compounds. The CYA itself blocks some of the UV and apparently does so over rather shallow depths. I'm reworking the theoretical model to account for this new data in this post.

This is what science is all about. Finding real-world data and developing a model that explains it or changing (or expanding or replacing) an older model to account for this data. I'm sorry I didn't catch that or question the industry data earlier. Maybe now we will be able to make rational recommendations on CYA levels, including using higher CYA levels in very sunny areas, though keeping correspondingly higher FC levels, and no longer thinking that this is less efficient (i.e. uses more chlorine) because we now know that it probably doesn't.

Richard