On Fri, 12 Mar 2004 21:02:03 GMT, "Coffee"
wrote:

Do these really work? Won't they harm the beneficial bacteria needed in the
filter?
Patty

http://www.aquaticeco.com/index.cfm/...Detail/ttid/80
Ultraviolet light can be very effective at eliminating viruses,
bacteria, algae and fungi. The required UV exposure rate to irradiate
common bacteria is 15,000 µW-sec/cm2, while the required UV exposure
for waterborne algae is 22,000 µW-sec/cm2. Since it is the intensity
of light that is doing the killing, we must know how much light energy
to use and how much is reaching the target. Just as some sunglasses
and sunscreens reduce UV intensity, so does discolored water,
turbidity, dirty quartz sleeves, and even some dissolved salts, such
as sodium thiosulfate. Even lamp temperatures can reduce output when
operated in cold water (110°F gives maximum UV output).

Page 449 of their 2002 hard copy catalog there is a chart giving
exposure for different micro organisms. Sorry I couldn't find it on
the web.

The bacteria attached to the filter is in no danger since it isn't
passing through the UV, but it may take a long time to build up on the
filter, I wouldn't know.

A fish farmer that used to hang around here mentioned they kill off
microaquatics eaten by hatching fry. So, if you use UV and want to
raise fry you need to feed them and he suggested boiled egg yoke.

Regards,

Hal