hard corals???
 

want to know about some of the difficulties and chlenges in keeping hard corals i will have a Coralife Aqualight Fixture PRO HQI 36 Inch 150 Watt
http://www.marineandreef.com/v/vspfi...RES53504-1.jpggetting cheep from craigslist for 150 bucks
and anything special that i might need to know about keeping them also8)

Depends on the coral you get, but you can check Coral Lighting and Acclimation for ideas on what you'll be needing as far as lights go. For the other paramaters you'll need
Good water quality Phosphates Untraceable-.3ppm and Nitrates Untraceable - 15ppm.
Good Calcium 400-500ppm
Good Magnesium 3xCalcium
Good Trace Materials
Good Alkalinity 8-12dkh
Great water flow and a good skimmer
Lights will be need in the good to great ratio if you want them to survive, but you also have to take the spectrum of the bulb into consideration as well.

15ppm is the most you can have, or your corals will be turning green... as in dieing. water quality is the greatest parameters that most hobbiest fail to get into line

To start with, you'll need RO/DI water to get the quality started in the right direction.