High light, high flow and low N and P is where mine grows the fastest.
I have to peel it off the overflow on a regular basis in this tank. Im not sure how much par the GSP gets but the blue acro up high is getting 500 par. The flow has the GSP whipping around quite a bit.
This is from a little piece I glued down. I can't remember how long it's been tho.
This is growing in less flow with much higher N and P and grows slower. Again no time frame, I just never pay much attention to when I stick a piece of GSP somewhere.
That said for the first few years i couldn't keep the stuff alive nut I have no idea why. I still can keep xenia alive lol