Design recommendations for an array of different forward voltage LEDs
I would seriously consider using a switched mode driving scheme to prevent wasting a ton of power in resistors and/or linear drivers, superheating your poor fish, upping your electric bill, and lining the pockets of greedy electricity companies.   There are a ton of application notes about designing them using DC DC converter IC's.  Depending on your experience, skill, and desire to make a project out of this, you could design your own, or buy one which already does this.

http://www.digikey.com/en/articles/techzone/2011/jun/buck-regulators-make-driving-high-brightness-leds-easy