# Watts Per Gallon?



## logan84 (Jul 27, 2011)

So I know I can just take the watts from my bulbs and divide by the gallons of my tank... but I've heard that to get an "actual" WPG calculation you need to take into account the amount of items in the tank such as the gravel/sand and rocks. 

While it makes sense to a point because of water displacement I'm seeing pretty much everyone going by watts/gallons in forums and other online communities. Does anyone else do this differently? 

Also I hear people claim that WPG was based on T12 days and beyond so the typical watts/gallons doesn't match up fully with today's T5 or T8. Any thoughts on that? I just read that someone who's sporting .75wpg is actually closer to, if not over, 1wpg as they were using T5 bulbs which are more efficient blah blah blah.

For something so simple I fear I'm making it absurdly difficult in my head!


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## jrman83 (Jul 9, 2010)

First off, what is your goal?

WPG works for T8. Everything else is a guess and it surely doesn't work with T5HO. No need to account for anything in the tank. Not really based off how much water is in the tank, but more the size of the tank, distance to gravel, etc.

I think if someone is splitting hairs enough that there is concern on .75 vs 1 or a little more, they need to take a breather. Whether or not you have enough light just depends on the plants you want to keep. If they are low light plants, the lower end fixtures will work fine. If you wanted higher requirement plants like many of the reddish stem plants, then maybe not.


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## logan84 (Jul 27, 2011)

No real goal - I was just curious because I was seeing different things online. Plus I wanted to make sure I just wasn't living it up on mega out-dated information.

I just have boring old T5s and one T8 providing my tank with light so I'll stick with the normal watts/gallon it sounds like!


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## BBradbury (Apr 22, 2011)

Hello logan...

If you want to grow aquatic plants, you need these: Light, clean water and food.

Most plants just need low to moderate light, .5 to 1.5 watts of light per gallon of tank volume.

Plants need very clean water. 50 percent of the tank's volume changed weekly.

Plants need a source of macro and micro nutrients dosed weekly: The macro come from the water changes and the fish. So, feed the fish a balanced diet.
The micros come a commercial source either powder, liquid or tablet.

That's it. Pretty simple.

B


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## James0816 (Jun 19, 2009)

While the WPG rule is pretty old, it is still fairly common place to use to a certain extent. Definately so much has changed through the years with technology.

For shallow tanks such as 10g, 20long and similar, the rule really doesn't apply as the distance from light to substrate is minimal. Where the rule does come in handy at are the deeper tanks such as 20highs and above.

Other caveats include the bulb itself. From T12 to T5, you still do pay attention to the rule. It's not until you start looking at the T5HO and VHO bulbs where it can be scewed a bit due to the output. 

Then of course with new technology comes the trend of LEDs. Brings another dimension into play.

Objects in the tank don't really matter for anything other than shading. Everything is based on distance from the light source to the top of the substrate.

If you want actual tech results, then you want to use a PAR meter instead. But that gets too techy for me so I just play it old school. )


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