Here's a thought for you, the shimmering effect you are talking about is caused by a "point" light source as opposed to a diffused type like a flourescent tube. Since you are talking a fish only tank you might want to check out the SoLux brand of halogen lights. They are available in different color temps but they have them in 4700K which is basically daylight. I have never used them on a tank but have them at work in a showroom for color samples on furniture. They are also low voltage (12 volt). The bulbs cost like 8-10 bucks. Couple of the clip on light fixtures from Ikea (the ones with the transformer built in) for like 10 bucks each and a ten dollar bulb, Hmmmmmm, bent with two of these set up you could get some shimmers, hehe. And, if it don't work out you got a couple of nice accent lights for around the house.