I would try for more lighting. It's been done with 2x9w, but it's certainly not ideal. Try to find something with more than 18w.
Yes, you're right... they come with 50/50 bulbs. I have the bulbs swapped out to one 6,700K and one 10,000K bulb. I had the bulbs left over from another project that I figured I might as well use.I thought the Coralife 12" Aqualight 2 x 18W comes with 50/50 lights. So you replaced it with 6700K or 10000K? Going that route for me might be a bit out of my budget.
My friend has an Odyssea 24W fixture, but I heard many bad stories about it, so I am not sure if it is good or bad.