How tall of a tank will a MH 150Watt work for?

[Whatigot]

hey man, welcome to the board.
I have a 24' deep tank with 2x150w 20k hqi halides and I found that my lighting was good to very good.

you might want to consider going with a 6700k or a 10k halide and then working some supplemental actinics into your lighting plan.
There is better par at depth with a whiter spectrum, so you'd be more likely to have success with sps or clams if you did it that way.

I would expect you might want to go for a 175 or 250 halide for the 30" depth though, depending on what you want to keep and where in your tank you'd like to place it.

cheers, from one noob to another.