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Re: UV - Philosophical Comments & Practical Facts

Ellen O'Connell said, in part:

> This is very much philosophical as I haven't used a UV,
> but . . . sometime 
> ago I read a post, perhaps to this list, perhaps to
> another, from someone 
> who had a large tank full of cardinal tetras who kept a
> UV running all the 
> time.  The bulb burned out and it took the person a while
> to get another 
> and get it installed and most (all? this is from memory)
> of the cardinals 
> died in that time.  That person's conclusion was that by
> conditioning the 
> cardinals to water pretty much free from all pathogens
> their immune systems 
> had been weakened to where they couldn't handle living in
> ordinary aquarium 
> conditions.  

This seems a not unreasonable hypothesis but a very rash
conclusion if that is all the evidence there is.  Aquaria
with UVs are not free of bacteria; the exposure to floating
bacteria is reduced, but not eliminated.  And anything that
isn't floating isn't zapped at all.

There might be very long term consequences from UV use that
relates to the competition amoung protozoan or bacterial
types -- whether that's beneficial, benign, or adverse, no
one knows.  But I doubt that turning one off in a tank
caused fish death by sudden germ exposure.  After all,
neons can be so fragile, who knows what prompted them to
perish?  And lots of folks have turned them off without
"sudden death."

Otoh, This fellow's tank might have had just such a
bacterium that was sufficiently abated by UV to not effect
the fish but which the remaining cells of which, after the
UV died, multiplied quickly and killed the fish.  Could
happen.  But without the UV, they would have died even
sooner, if that bacterium was in the tank an unabated.

Scott H.

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