Depends on so mucch lighting,current, tankmates, fish,.....
I have two 1 is middle of tank in low flow and the other 1 is on the bottom with med. flow under 440w VHO lighting.
The 1 in low flow has grow well in the 8 months I have had it and the 1 in med flow has only been around for a month but seems to like placement don't know how it will grow yet to soon to tell.