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 I had been looking at Rapid LED.  I guess I will just use their formula.  I was just hoping to gain some understanding on where the formula comes from and if it is accurate.  
 The tank I was planning for is a 20 high.  The other issue I had was the size of the heat sink.  I was thinking of going big so that I can distribute the light evenly but most of the lights you can buy are smaller so the light is mainly focused over the centre of the tank.
 
				__________________72g bowfront, t5.
 29g JBJ nano cube, ATI 26HD.
 
 Livestock: clown fish, chromis, coral beauty.
 
 Corals: Toadstool, maze brain, candy cane, mushrooms (purple & green hairy), button polyps, green zoas, GSP.
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