Lighting question

[bjohnston]

I have a Lighting hood with 3-250w MH and 2-96w actinic Flour. bulbs.
Two questions:
How many hours of use before these type bulbs should be replaced?
How high above the tank (210 Gallon 72x24x29in) should this hood be set? I currently have it sitting directly on the top of the tank and I don't know if that's appropriate.

 

[lando]

CF bulbs loose spectum after 8-9 months and should be replaced then. MH can go 12-15 months before they need changing.