[APD] 2x175W Metal Halide and 72" Tank (135G)

[Jerry Baker <jerry at bakerweb_biz>]

I am in the planning stages of a 135G planted tank. I previously had a 
75G planted tank that was a resounding success. On that tank I had 4x55W 
compact fluorescent from AH Supply. The plants did great. Everything 
from rotala to ludwigia were colored well.

I am thinking of going with MH for my 135G tank (72" x 18" x 24"). 
Keeping in mind that my previous tank was running 220W for 48", it 
seemed reasonable that 350W for an additional 24" should cut it. That 
makes 2 x 175W MH, but I have seen it recommended that you have one MH 
for every 24" of tank length. Since electricity costs me 11.9 cents per 
kWH, I am not keen on having 525W of lighting running for 12 hours per 
day. Not to mention that I probably won't be able to use my microwave 
while that setup is running without tripping a breaker.

Anyway, I want to know how bad the "dark spot" in the middle would be if 
I placed only two 175W MH hood-mounted retrofits over a 6' tank. Of 
course, each would be placed 18" from the ends of the tank. Would it 
really be so bad? My plan is to have a rather large sword somewhere in 
the middle, and since they don't need a lot of light relative to some 
other plants, this shouldn't be too bad. Am I off base?

If someone has a 6' tank with only two MH over it, I would love to see a 
picture so I could get some sort of idea.

Thanks.

-- 
Jerry Baker
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