Do you have any pictures?
When and how are you trimming?
When I started with this plant it looked like:
Then it looks like this before trimming:
One Month Later with trimming and replanting the trims it looks like:
I've been trimming the longer ones and just replanting, It's a process with this plant I'm finding, where I've been trimming some side shoots are coming out so it's thickening up and you see what it looks like, soon I will be trimming and replanting again....
As for tank specs you and I are close, only I'm a 55 gallon and I run my 2x54w t5HO on a 4h on, 4h off, 4h on, 8h off light schedule