Geranium Putting Out Roots

I was dusting the window the other day (useless task to avoid studying) when I noticed that one of my little geranium cuttings is putting out some nice roots.

Not sure if this is the variable that's making a difference, but the one that's growing better is in an olive oil bottle (bigger) as opposed to a spice jar (smaller). Every time I change the water in the spice jar there is a thin layer of greeny film on the bottom. I'm wondering if the smaller volume of water is allowing the mossy stuff to grow faster and somehow stunt the growth of the cutting? Of course, I have no scientific basis for saying that, but it's just my hunch.