Merk, there is no way I would even waste time on this if I felt it would cost me $300 - my wife would kill me! So, while I agree with what you are saying, I'm still looking for a way to get down to around $150.
Regloh, I agree about the refraction, but most of the light will enter the water close enough to vertical for refraction to make little difference, especially given the overall inaccuracy involved with this.
Wasserpest, I agree about the T5's too, but if I go ahead with this, it will be in part to avoid having to buy new bulbs, and it is an opportunity to study up on a new subject for me. As usual, the more I learn the less I find I know! The problem with using more LED's with lower power is that the cost doesn't drop as fast as the power, so I end up again with a $300 fixture. Tonight I started studying the Cree website, and I'm still at the utterly confused stage. A couple of good resources I found were
http://www.highend.com/support/training/lightingfaq.asp and
http://www.theledlight.com/technical.html A couple more weeks and I may understand the subject a little better.