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Re: Depth of Marine Tanks

> From: Jayme Donnelly <Jayme_Donnelly%BOND__NOTES at notes_worldcom.com>
> One other question.  If depth is not important, then why are salt water/reef
> aquariasts concerned with depth and what type of lighting they use to 
> "insure sufficient lighting reaches the bottom"??  Is it perhaps that certain
> type of lighting are better at penetrating obstacles in a tank than others, 
> since our tanks are not empty?
> 
> I have read that unless salt water/reef aquariasts are using a fairly shallow
> tank, then they use more intense lighting (e.g. Metal Halide, Mercury Vapor?)
> to reach the inhabitants of the tank.

I've been studying marine systems for a while now.  Yes, of course,
you are correct:  certain wavelengths are better at penetrating depths.
In general, the blue end of the spectrum is able to penetrate to a 
greater depth than the red end of the spectrum.

Another issue.  Because the specific gravity of marine water is so
much higher than freshwater (all those salts in there), it can better
suspend particles (organic matter or other plankton), which would
decrease the transparency of the solution (as compared to freshwater,
where things would "fall out" more readily).  Most fish are good at
seeing close up, not far away merely because visibility is impossible
at more than a relatively close distance.

I think this also accounts for the higher species diversity in marine
systems over freshwater systems:  more nutrients or "building blocks"
exist in marine systems from which carbon based life can draw.  That's
just a personal opinion, though.

I think Wright's statements on the marginally deeper tanks (2" not
a lot of difference), but I don't think there's any argument that
2" of marine water would resist the passage of photons MORE than 2"
of fresh water (higher specific gravity, dissolved solids, suspended
particles and OM, and plankton in marine).

--charley                           Fort Collins, Colorado USA
charleyb at gr_hp.com	or	charley at agrostis_nrel.colostate.edu