how high to mount mhs

[bdr]

I just bought a diy 2x 250w mh setup one 14k mogul base and one 20k mogul base. how high over a standard 75 gallon tank should I mount them?

 

[pete33]

I'm using 1 250w and have it 12" above the aquarium.

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[williewilliams]

mine are at 14"