Well the watts per gallon depends on a couple things. Like depth and type of bulb. The watts per gallon, rule doesn't quite apply to t5ho because the lighting is so intense. Depth is a factor because the shorter the tank the more intensity reaches the substrate.
What type of lamps do you have, and what is the spectrum or the k rating? Yes glut is Glutaraldehyde. Also the higher the light the shorter the plants. I have had dhg in 1 of my tanks for 4 months now and it might be 2 inches tall but it has been carpeting like mad. I haven't had to trim it at all.