As cmor mentioned, for a 24" deep tank, you want 250 at least if you are going with MH
. The is a huge different in both PAR and heat between MH
has way more PAR and also puts out way more heat. You get the least light penetration thru the water with reg flourescents, more with compact flourescent, then VHO
, good penetration with T5HO and the best is MH
It really comes down to what you ultimately want to keep. If you want to be able to get anything and not worry, go with MH
. If you want to save a few $$, add to your VHO
's and you should be good for almost anything.