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Subject: Light loss at Aquarium Depths

Pete Mohan wrote:

>     I don't think that loss of particular wavelengths is going to be much of
>a problem  because the path length of the light through the water is very
>short.  However, artifical light levels decrease with depth much more
>dramatically than light would in a natural environment.  Since this is a
>function of the inverse square law, it's a more serious problem with light
>sources that behave more like a point source. 

I thought the inverse square law was only pertinent to the distance of the
light from the water surface... that this was the light lost through air.  No?

> I've measured "natural" surface
>light levels under a metal halide (1000 watt), only to find out that at a
>depth of 30 inches the available light is similar to a 200 ft depth (that's
>two zeros...no typo <G>). 

What causes this much greater fall-off within a tank?

>The fall-off in light intensity is least problematic
>when the whole surface of the tank is covered with fluorescent lamps, but I
>haven't measured the actual loss with depth. 

This would seem to mean that watt for watt, you get better lighting from
fluorescents than from point source lighting like MH's.  Am I reading this

Subject: The Pits

Michael Schmidt wrote:

>>From what I have read here and elsewhere, having a tank get hit with all
>sorts of problems at once is not uncommon. Well, my tank's there right now.

It appears not to be uncommon, but it should be... it's preventable.

<snip long tale of BGA and a sick Oto>

My advice on the sick Oto is to euthanize it.  You will probably not save
its life in a hospital tank with medications, and in the mean time it could
infect your other fish.  

>Finally, my tank was looking suddenly cloudy this morning. Not
>green-cloudy, just cloudy. What is this stuff, any ideas? (I have a half
>dozen ideas, none convincing.) I understand my options are either a
>polishing filter ($$$), some of that commercial clear-water treatment ($),
>or just waiting for it to go away on it's own. Any recommendations?

Probably a bacterial bloom in response to you suppressing you bacterial
filter with antibiotics while feeding nitrogen products into your tank.

Stop tossing chemicals into your tank, sit back and wait a bit.  If your
plants are growing so quickly that you _really_ need to add nitrogen, it
might be preferable, particularly in such a small tank, to cut the light
and slow the growth down.  Remember that adding things isn't the only way
to bring things back into equilibrium.  Sometimes backing off on something
can do the trick just as well.  The goal is to provide just enough for the
needs of higher plants, while limiting what is available for algae growth.

Karen Randall
Aquatic Gardeners Association