250w or 400w MH for SPS Tank?

[Ira]

So, I am having a 36x24x24 tank built, and I am thinking about putting a MH fixture over it (or a 10x bulb t-5).

What is the main difference between these wattages, and which would you choose for your tank, and why?

Thanks!

 

[franklypre]

I have a 36X18X24 and have run 400w and 250s, personally I liked the 400 20k for growth and color. That said it puts off quite a bit more heat in the summer here so I run a 250 with LED supplements.