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light longevity, trace metals and NaHCO3.


First an observation/question...

About 2 1/2 years ago I installed several Philips C50 bulbs on two of my
tanks.  I was pleased with the light quality.  The lights over one tank
were in relatively inexpensive shop lights and lost a lot of intensity
within a couple months (I know some drop is normal, but this was
abnormal).  The other lights were in a much more expensive ceiling fixture
over a paludarium.  I just changed out the lights in the expensive ceiling
fixture and found the new lamps do be almost indistinguishable from the
old ones in intensitiy.  A sharp contrast to the dim and dying lights in
the shop lights.

Have other people had problems with flourescent tubes in cheap shop lights
fading prematurely?

***********************

 Michael Schmidt wrote:

> > Many earlier
> >analyses - including virtually all analyses included in our big public
> >data bases - were collected with methods that may have allowed the samples
> >to be contaminated with copper or zinc.
>
> I'm having a hard time imagining this. What I do find easy to imagine is
> that the "free" Zn and Cu was overestimated because the samples were
> collected without ultrafiltration or high-speed centrifugation. Suspended
> bacteria in "clear" water samples will be atomized in an atomic absorption
> spectrophotometer, and one obtains a signal for the metals they contain. (I
> had my students do this with some pond water this semester; turns out that
> in some "clear" centrifuged samples, 80+% of the Fe can be removed by
> filtration with a 0.2 micron filter, suggesting that it was incorporated
> into bacteria, other living things or colloids to small to be centrifuged
> out at moderate speeds.)

This is pretty tangential, so I'll try keep it brief.

The SOP for water samples by USGS, EPA and state water quality agencies
(at least those I'm aware of) uses a 0.45 micron filter.  There is a metal
content in the size fraction between 0.2 microns and 0.45 microns and that
is one of the problems with older data.

There seems to be a complete gradation from dissolved metals through metal
hydroxide complexes into polymers, colloids and amorphous and/or
microcrystalline precipitates.  Different filter sizes divide that
gradation more-or-less arbitrarily.

I read one paper that stated the toxicity of metal hydroxide complexes
(Cu, I think it was) was actually greater than the toxicity of the
unassociated metal.  I don't know if that is reproducable or not.  The
possible role of larger complexes up to colloidal sizes in toxicity and
bioaccumulation are (to my knowledge) not resolved.  So when we start
looking at concentration differences caused by filter sizes we may or may
not be looking at differences that are biologically significant.

I have a copy of what I think is a preliminary EPA document dated
10-1-93 and titled "Appendix B.  Guidance Concerning the Use of 'Clean
Techniques' and QA/QC in the Measurement of Trace Metals" (author
unknown).  Quoting:

	"The U.S. EPA (1983, 1991) has published analytical methods for
monitoring metals in water and wastewaters, but these methods are
inadequate for determination of ambient concentrations of some metals in
some surface waters."

An article by Shiller and Boyle (1987) compares data from the EPA database
to results with more exacting methods.  Sorry I don't have the full
reference.  Couldn't find my file :(.

**********************

Jim Wilson reposted:

> >Is there a benefit to adding CaCO2 to raise my KH instead of NaHCO3?
> >I know that CaCO2 also raises GH.
>
> OK OK I'm the best typist in the world and do know that it is CaCO3 and not
> CaCO2.
>
> But did I stump the panel?  Or has this question been answered too many
> times already?
>

NaHCO3 is more readily available in a fine powdered form (baking soda) and
it dissolves more easily.


Roger Miller