Hey there everyone. I dont know if im going to get this soon or later. Maybe next year. I just wanted to plan out first. Well Im going to be ordering 1 400watt ballast and dual it to have 175watt bulb on each side for my 55 tank. Ill be running 65 watt Atinic PC with it too. Here are some pictures of the ballast that I might buy.
I would like to know which of these ballast is better.

Choice one:http://item.express.ebay.com/400-watt-MH-Grow-Light-BALLAST-KIT-400w-METAL-HALIDE-w_W0QQitemZ180037360307QQihZ008QQfromsoiZ1QQcmdZExpressItem

Choice 2:http://item.express.ebay.com/NEW-400-watt-HPS-Grow-Light-BALLAST-KIT-400w-Sodium-w_W0QQitemZ180037360301QQihZ008QQfromsoiZ1QQcmdZExpressItem

Which is the best? And why are they different prices when they are the same watt. I was planning on getting one and dual it to carry 2 175 watt bulb for my tank. Thanks.

The difference in cost seems to be due to the included ignitor in the HPS kit. On one site I checked, they cost under $9.00 a piece.

Which type of ballast is better, I am guessing, would be what you are going to do or want to accomplish.

Here is a Wikipedia link for sodium lamps.
http://en.wikipedia.org/wiki/Sodium_vapor_lamp

Here is one for the metal halide lamp
http://en.wikipedia.org/wiki/Metal_halide

There is a pretty good description of the lamps, what they do, how they work, and what they are typically used for. I hope this helps you decide which you prefer.

Thanks FF. Really good articles there. Im guessing Ill just go with the MH set and not the HPS set.