The decision between 24/0 and 18/6 is really iffy. There are many rumors about faster growth with 24/0, but also many people believe that 24/0 cause hermies. As far as I can tell, no one has a damned clue, so do whatever you want. My personal opinion is 18/6 just because it seems so unnatural to have 24/0. I'd always rather stay closer to what nature does.