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(I don't know whether this belongs here or in technical tinkering, but I'll post here since UV filters are mostly used in ponds.)

I've read that you should replace the bulb in your UV filter every season. But do you think that's really necessary? Is there a way (aside from algae growth) to tell when the bulb isn't doing its job any more? Does it get dimmer or burn out? Or does it stay as brightly lit as ever but become less effective? (And if so, why?)

I replaced mine, like a good little camper, when I started my pond up for the season, but dang, those bulbs are expensive! And the old one seemed to light up just fine, so I'm wondering whether I fell victim to a manufacturer's get-them-to-spend-as-much-money-as-possible ploy ...

Hi,
Unfortunately, you have hit on the "problem" with UV
systems. They are expensive to purchase, and to upkeep.
Yes, you do have to replace the bulbs at the interval
recommended by the manufacturer. Most are every 6 months.
All of them develop cleanliness problems, and most can
be taken apart and cleaned. DO NOT touch the bulb with
your fingers. It's a form of quartz or a special glass.
If you touch the glass sleeve or bulb the oils from your
fingers will transfer to the surface and concentrate the
heat from the bulb. That causes the glass to soften, and
it will bulge at that point. In some cases the deformity
is so severe that you will not be able to take the system
apart to change the bulb. Do not look at the bulb when
it is in operation. Don't even peek at it through a
crack in the plastic to see if it is working. The UV light
will damage your eyes. Most are covered so that when
they are in operation, you can see the glow of the bulb
when the room is dark.

The bulbs put out light in a specific part of the spectrum.
As bulbs burn (any type of bulb) they have a "burn in
period" during which they start at one "brightness" and
then settle in to a constant, slow, rate of decay. In the
UV light case, while the filament continues to burn, the
light is no longer the right frequencies and all it is
doing is furnishing light, still high frequency, but
not killing as it should.

Flourscent bulbs do the same thing. They have a burn in
period of about 100 hours, and then depending upon the
type of bulb and the phosphors that are used, the light
slowly dimms till it ceases to function. In planted tanks
the flourscents should be changed at an annual basis.
metal Halides on a 6 -8 month interval.

Sorry, change the bulb.

Frank


Last edited by FRANK at 12-Apr-2005 09:36

-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

Actually, that reply made me very happy! I'd already changed the bulb, but was wondering whether I was a sucker for doing it. Also, I never really understood the "don't touch the glass" thing ... now I do.

So thanks!