# [APD] Re: how much light?

```Dave Grim writes:
>1. Just because a manufacturer says
>the tank is 240 gallons, it is not
>necessarily right on the money.

How true. Based on scientific research and years of experience, I have
decoded the secret of MSTS (Manufacturers Suggested Tank Size). The MSTS
is not actually how much water the tank will hold but instead is the size
of the shipping container that would be required if aquariums were shipped
in shipping containers, which they are not. To determine MSTS, measure the
extreme outside dimensions of the tank, including plastic trim if so
equipped. Multiply length x width x height and divide by 231 (U.S. readers
only). Of course, the "231" number is only a suggestion; some
manufacturers may go as low as 225 in MSTS calculations.

>3. The amount of water in the substrate
>is minimal and shouldn't be considered
>in calculating watts per gallon

As luck would have it, I have also done extensive investigations into
Substrate Water Displacement and Substrate Volume. Available data only
applies to TexBlast substrates.  TexBlast is 6x16 mesh quartz sandblasting
gravel (a grain size of around 1/16" to 1/8"). This same gravel can also
be found as pool filter sand.

A pound of TexBlast has a volume of about 19 cubic inches.  This is useful
if you want to calculate the amount of TexBlast needed for a particular
depth of substrate. For example, suppose you wanted a 4" deep substrate in
a "90" gallon tank. The interior dimensions of the tank bottom are 47" x
17". So, (47 x 17 x 4)/19 = 168.2 pounds of gravel.

TexBlast will displace 0.048 gallons of water per pound, so the example
substrate above will displace 8.07 gallons of water and should be
subtracted from the Actual Tank Size. For example, consider the same "90"
gallon tank with a water level 1.5" below the topmost extent of the rim
(22.5" from the tank bottom). The Actual Tank Size is (47x17x22.5)/231 or
77.8 gallons. Subtracting the water displaced by the substrate gives a
True Water Volume of 69.8 gallons. Yow!

As for "the amount of water in the substrate is minimal", I'll let you
draw your own conclusion. The volume of the example substrate is 13.84
gallons and has 5.77 gallons of water. So the substrate is 42% water by
volume.

Other substrate materials such as Fluorite will not have the same
characteristics.

With that settled, we can now return to the enjoyable "something really
new and innovative on the APD" to keep Karen happy :-)

George Booth in Ft. Collins, CO (gbooth at frii dot com)
The website for Aquatic Gardeners by Aquatic Gardeners
http://aquaticconcepts.thekrib.com/  (mirror)
http://www.frii.com/~gbooth/AquaticConcepts/

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