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Re: Effect of UV sterilizer on biological filter

Arturo Batista asked if a UV sterilizer would affect an aquarium
system's biofilter:
> while doing maintenance today I noticed that the tank has 1 PPM
> Ammonia.
> This is a long ago cycled tank; Nitrites are 0; Nitrates 8 PPM.
> I do a partial water change weekly or so, with the last one 3 days
> ago
> (15 Gallons out of 55 gallons).
> Could this be caused by the UV sterilizer, or perhaps because when I
> did
> the water change I also changed filter media 

The UV lamp can only kill what is directly exposed to it, and then,
only if exposed for a sufficient amount of time.  So the bacteria in
your substrate, filter media, on your driftwood, glass, etc. isn't

Not even all waterborne bacteria are likely to be killed since filtered
and unfiltered water keep mixing as the filter runs *and* bacteria keep
growing during that time.  After the many hours it typically takes for
nearly all of the water to run through the filter and UV, lots of
bacteria have been created.  If the "turnover" is fast enough, you can
"get ahead" of the bacteria, but the UV won't ever hurt was doesn't
pass through it.

When you through out your filter media, you throw out a lot of bacteria
along with it.  That's and argument for using two smaller filters,
cleaned on alternate cycles, rather than one large one.  But, that only
matters if the filter media that you change is the predominant
biofilter.  There's some bacteria just about everywhere else in the
system (unscientifically speaking).

Scott H.

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