I squirt a couple of mls EasyLife EasyCarbo directly on thread algae infested weeping moss without it minding it at all. It's hard on the algae though.
I'm not completely sure EasyCarbo is the same thing as Excel though.
It grows java moss quite nicely based on my exp with 3 tanks with it over 1.5 yrs. I had some pellia growing with it but then it died out. wasn;t sure if that was the ferts being off or a fish eating it