I think that should be just fine. Aquactinics makes a very good T-5 fixture. I've kept a crocea at pretty close to the same distance (10" under water, but the light was further from the surface) under a lesser quality fixture (4xTek T-5) and it did very well. People who don't have much knowledge of T-5s may tell you things like you don't have enough watts per gallon, but I wouldn't pay any attention to those comments.