One more time on WPG...

Ok, I know the WPG is not 'in' anymore (or ever was correctly), but I was wondering if based on that theory...if you put a 48" PC on a 72" (125 gal - 72x18x22) tank and only place corals under the light (meaning only the 48" that's under the fixture) where the volume of the water is roughly 82 gal.

So, this area (82 gal) would have ~4.7 WPG when a 48" 384 watts PC is used...correct?

Thanks!
GKW

 

I'll be interested to see what other people have to say about this, too. It seems to me that you would be correct, and that if you placed corals in that area only, they would be fine as long as they were probably closer to the top. Especially for more light demanding ones. But that would kind of suck to limit your coral space to only that area, in my own opinion anyways....

 

I would not chance any sps

 

Once again, I would make my decision based on the depth of the tank.
It looks like you have a pc fixture that is 4 x 96 watts with probably 2 daylight or 10k bulbs and 2 actinic bulbs?? Lighting up a 72" long tank that is 22" tall.
You can use NO bulbs if you want and thats all you have. Your fish will be happy with all that light. Any type of light demanding corals will not be happy and probably not last for long. So, what is your question
Will the light work? Most certainly it will. It will even look nice.
IMO Don't try any Clams, SPS or light demanding LPS.

Jim

 

The 72" x 18" x 22" and the 4x96 pc was just an example. How about MH for example, taking the height out of the equation, you can use ONE MH over a 8 feet long tank and only put corals under that MH (which is ~2 ft) and still works for clams or SPS.

Same thing with the PC/T5/VHO, it doesn't matter the volume of the whole tank, all it matter is the corals will get the PAR from the light and from what I understand is that PAR don't spread. So, over a 6 feet (125gal) tank, if you use a 4' lighting fixture (PC/T5/VHO), it will actually be over a ~82 gal of water, which is ~4.7 WPG.

That's the way I see it and I think alot of people are misunderstanding the WPG thumbrule. You don't have to get a light fixture base on the volume of water of your whole tank, only the area/volume of the light fixture is under (considering if you don't put any corals on the side of the tank where are not hit by direct light).

Any comments/correction?

 

The WPG thumbrule only works for someone who does not understand the different types of light sources and how they penetrate the water into the tank.
The thumbrule (lol) for metal halides is, use one per every two foot of depth and length. Then adjust for depth of tank by getting a higher or lower wattage.
A PC fixture that is 48" long will generally cover a 48" long tank. It will give some light to a longer tank but not much.
If looks you're trying to make a wpg thumbrule based on gallons of water under the lights. It doesn't work that way, The only way it would work...
Take all the other variables out of the equation. There's only type of light and it only comes in one shape.
What more can I say.

Jim

 

Yeah, I guess that's what I was trying to say...the light penetration.

I have a 125 gal tank w/ only 110w PC and 70w NO, that would fail the WPG rule. But I have the 110w PC over the center 22" of the tank and my corals are growing. That's why I was wondering why people are saying I should not have corals in such a low lighted area...we proof them wrong!

Thanks!

 

What if you were a nutrionist and I asked you how much vitamin C was in an orange compared to a tangerine or a grapefruit. They are all different types of citrus fruits with slightly different nutrients, but all in the same family....
maybe I am drawing a bad analogy. :
If you insist on a wpg rule then you would have to create one for each type of light source. One for metal halides, one for vho's, one for pc bulbs and one for T5 HO and NO bulbs.
Sorry, for appearing to make this complicated. But it is and I don't think you can make sweeping generalizations and be succesful.
Quit making me use my brain.

Jim

 

lol, yeah, it is complicated. Some people argue w/ me about that and they still think I am cruel for putting corals in my tank to die....AFTER 2 OF MORE WEEKS I HAD THEM! I told them to come here, but they think they know all about marine aquaria and don't need this. O, well, I tried.

Brain...shutting down....