Danny,
I think it depends on a number of factors. Lighting, keeping chemistry up to snuff (alk, Ca, Mg), possibly low nitrates. The massive orange cap in the 37g (24" high) was started about a year ago from two toonie sized frags and kept under a single 6500k MH until two months ago when I changed the lighting to 14000k ARC MH. Can't tell if it's grown much, but that may be because it's so big already.
Am closely watching the green cap on the left side of the towering rock. It's growing quite well. There are other, much smaller green cap frags on that same rock. They were kinda frags of frags and have taken a bit of time to establish their "growing edges". These are the frags that I believe poisoned me wuth their slimy edges
