Re: [APD] Re: how much light?

["S. Hieber" <shieber at yahoo_com>]

--- Dgrim62 at cs_com wrote:
> This has been a very interesting thread to read, as I
> have been playing with 
> light levels in my fairly new 240 gallon tank, which up
> until a week ago had 
> four 175 watt metal halide lights about 12 inches above
> the water surface. My 
> tank is 24 inches tall. I was having a very hard time
> with a couple different 
> types of algae. > 
> Here are my errors (IMO): 

A 240g! Now that's a tank with some elbow room for jungle
farmers like me, who is stuck with a measly 150g tank
(nominal size).

> 
> 1. Just because a manufacturer says the tank is 240
> gallons, it is not 
> necessarily right on the money. The best way to get the
> actual gallons in your tank 
> is to measure and multiply the tank's inside length x
> width x height in inches 
> and divide by 231 cubic inches in a gallon of water. That
> will give you the 
> actual gallons in your tank.
> 
> Some tanks are manygallons less than the label may say.
> 
> 2. I stopped using the gallons in my sump to determine my
> light level. That 
> amount of water never sees light anyways.
> 
> 3. The amount of water in the substrate is minimal and
> shouldn't be 
> considered in calculating watts per gallon, as this
> significantly inflated the volume I 
> was thinking was in my tank.


Being fond of rules of thumb, because they are easy to
remember, easy to pass on, and generally practical, I
measured a few tanks, adjusted for substrate -- never
counted sump water but just the size of the space being lit
-- and decided that a reasonably good figure to use is 80%
of the manufacturer's stated nominal size for the aquarium.
 (Has anyone found a tank whose internal volume was larger
than the nominal size?) Yes, there's lots of variance and
wpg is only a rule of thumb itself since bulbs, reflectors,
ballasts vary. 

So is a wpg rule of thumb based on nominal or actual
volume? I guess you'd have to ask each person that states a
wpg rule. One could express a rule either way.  When I do
it, I have in mind the nominal size because it's one less
thing for folks to have to measure and compute. But even
the 20% adjustment, wouldn't get my rates quite down to
George's levels. 

Of course, I never said anyone *should* have a high light
level of 3-4 wpg. Or that someone should have a high light
or low light or fast grow or slow grow aquarium. I have
diff kinds and find them all intersting, each in somewhat
diff ways. But I think there's a diff between my view and
George's. He seems to think more than 2.5 is inappropriate"
whereas I think it's high, doable, harder to maintain a
tank at that level but lots of folks seem to do it.

Scott H.

=====
S. Hieber

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