wouldn't it kill algae spores and not allow the algae to spread in the tank
as easily?

Not by my experience. UV sterilizers don't actually make the tank sterile.
Some people claim that the fishes' immune systems get weak, because there's no
germs to keep them revved up. Or that they kill off the biological filter.
Not true. There's plenty of bacteria, spores, and the like in a tank with a UV
sterilizer on it.
The UV sterilizer can only kill the stuff that's free-floating, and it doesn't
kill 100% of that.


Leigh

http://www.fortunecity.com/lavender/halloween/881/