I have the variety that has a lot of red in the upper portion of the stems, it's the Rosengiv variation I beleive.
Anyway, it always grew very fast and always required trimming when I had it in my 20, with DIY CO2 and 2.4 WPG and ferts, but since put it in a 10 gallon with those Spirally daylight CFLs, and Excel and ferts, it grows much slower and still displays it's beautiful red color.
Much easier to keep. I am happier with it in it's new environment.
I had the same experience! I put it in my "low tech" tank with no CO2 and less light, using only Excel and ferts. It grows beautfully in it's "stunted" form with smaller leaves, creeping along the bottom, and it has a really nice pinkish red color.
Paul