Needing some more information on UV

[PoolDoc]

Hi F;

[ EDIT: just noticed your SWCG and tree worries. Salt water from pools is a potential problem ONLY when it's not diluted, but is concentrated by evaporation. While that can happen in Texas, the situation you describe -- overflows from rains -- is the EXACT opposite of the problem scenario. If there are heavy rains, any salt runoff will be so diluted that it's a non-issue. In fact, even when undiluted water from salt pools has gotten on lawns, it doesn't seem to be a problem. However, I don't think I'd recommend repeatedly discharging the backwash from a salt pool filter at the base of a tree you wanted to keep. ]

I have limited time this weekend. I did check your links, before removing them, and you are correct that most of the solar radiation that reaches the surface is UV-A. (The ozone layer apparently stops most of the UV-C). It's not quite true that UV-A is not germicidal, but it's certainly not as effective as UV-C. However, it's not at all clear to me that UV-C is in any way effective against algae, or algal spores, which are a huge issue on OUTDOOR pools.

I deleted your "Ask Alan" link, because the page appared to be simultaneously providing information about UV in pools and doing paid ads and links to Delta UV, AND because there were some very serious errors in the statements made. I hope I'll have time to get back to this, but I'm not promising anything.

It's sort of a 'niche' question, and a rather tiny niche at that. Even if I take at face value the 10,000 pool number, that would be 10,000 out of about 10,000,000 pool owners in the USA, based on stats I've seen over the years. In other words, 99.9% of the pool owners out there are NOT interested. But, I'd bet those numbers from DeltatUV are (a) rounded up, (b) aggregates of ALL UV purchases over the last decade, (c) 90% indoor pools, and (d) not adjusted for the folks who bought, and then abandoned the UV units. If there are 100 *active* users of UV on *outdoor* pools in the USA, I'd be surprised.

UV does have some reasonable applications on INDOOR pools, and is being used commercially to resolve some specific problems. But to use UV on an outdoor pool on the theory that it might save money is wishful thinking.

However, Chem_Geek actively investigates all sorts of alternative systems, so I'll email him and see if he wants to take a look at this.

Good luck!