Watts per gallon? - The Planted Tank Forum
 
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post #1 of 7 (permalink) Old 09-23-2004, 07:31 AM Thread Starter
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Watts per gallon?

OK - we'll just cut to the chase.....

I have a 90 gallon tank that has 4x65watt CF lights. The easy calculation would be...
(4x65)/90= 2.9 watt/gal

However, I also have 160+lbs of EcoComplete sucbstrate and one BIG piece of driftwood. The two items together displace approximately 10 gallons of water. So the question is... what should I use for the most accurate watts/gallon? The above formula... or the one that takes into account the displaced water - which would be...

(4x65)/(90-10)= 3.25 watts/gal

It's not like these figures aren't close, and I know that watts per gallon is just a ruff idea of lighting. I'm just curious how most people would do this computation knowing the specifics of my/their tank.

Thanks in advance for your time

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post #2 of 7 (permalink) Old 09-23-2004, 11:05 AM
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The watts per gallon rule is just a rule of thumb, nothing scientific or at all calculated to accurate measures. We always have been using tank volume, not water volume. This is more logical too, because who is not to say someone filled thier tank only half way? It should not mean they do half the watts too, they still have the same volume of space to be lighted.
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post #3 of 7 (permalink) Old 09-23-2004, 12:32 PM
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With your lighting on your tank you should be able to grow pretty much anything you want. And isn't that what really matters?
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post #4 of 7 (permalink) Old 09-23-2004, 06:54 PM Thread Starter
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Well, my main confusion is when buying new plants or reasearching before I buy them. Most every store rates the plants as either low, medium, or high lighting requirements - some break these down further as < 2watts/gal being low, 2 to 3watts/gal being medium - and greater then 3 watts/gal being high. Basically I was trying to arrive at where I stood in the rankings.

Quote:
Originally Posted by Rex Grigg
With your lighting on your tank you should be able to grow pretty much anything you want. And isn't that what really matters?
Yes

Thanks for the advice

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post #5 of 7 (permalink) Old 09-23-2004, 10:44 PM
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Sn8k

LOVE your tank. Quite the thread!

Keep in mind that a 90 gal is particularly deep. For this reason you may want to think about watts per square foot. A typical 55 gal is 48x13x20 and yours is reported as 48X14X30.
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post #6 of 7 (permalink) Old 09-23-2004, 10:56 PM
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Go ahead and Order away... the only plants that wont grow under those bulbs are plants that are shaded by others. If they are kept in a lit area there isnt anything you cant grow.
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post #7 of 7 (permalink) Old 09-24-2004, 12:27 AM
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Those recommendations by the store are very misleading but commonly used. In fact I think I may have used them once or twice. There is a huge difference between 2 wpg over a 10 gallon tank and 2 wpg over a 125 gallon tank.
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