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Re: UV Sterilizer

Paulio629 at aol_com asked:

> How effective are these in fresh water and how long do the bulbs
> last?

They can be very effective at killing algae that is afloat, protozoa
that are afloat, bacteria that is afloat.  Only things in the water
that passes past the bulb are killed by the radiation.

If you mean how long until they burn out (i.e., one of the filaments
breaks), probably a year or two if you leave it on 24-7.  If you cycle
it on/off often (say, every three hours) then the bulb might not last
even half as long.  If you cycle only twice a day, it will probably
last longer than running 24-7 before the filaments burn out.  If you
only use it one day a week for 24 hours or so, the bulb will probably
last you so long, you won't remember how old it is and you'll just
replace it on general principles after a few years   ;-)  .

If you mean how long does the bulb remain effective, then that depends
on what you are using it for and how large the bulb is.  Like
flourescent bulbs, UV bulbs degrade with use.  Only a small percentage
of the energy used is actually converted to useful UV light -- for a 15
watt bulb I think its about 4 watts of of useful UV -- that purple
visible light that they give off isn't useful UV is merely V.  The
amount of useful UV gets steadily lower the longer the bulb is used. 
*But* how much that matters depends on bulb size and what you are
trying to kill.  Algae are killed with much less exposure than protozoa
(e.g., ich).  If you only want to kill algae, then you don't need a
much exposure so a bulb can be used longer, other things being equal. 
Alternatively, you could use a smaller bulb to start with instead of
using it longer.

You should check manufacturer specs for the best wattage for a given
target (algae or protozoa), tank size, and waterflow.  Based on that, a
bulb is usually rated as good for about 12-18 months depending on the
maker and wthether their model uses pc bulbs, T5s or t8s or t12s.  An
oversized (wattage) bulb can be used for a proportionately longer time
without replacement -- the economics vary from case to case.

If you get a UV lamp, I suggest you get one for which it is easy to
change bulbs and easy to clean.  Also, check out replacement bulb
prices before you decide which one is the best bargain.

Hope that helps,
Scott H.

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