Jeff is right - algae is bad. The smaller your container, the worse it is. In the wild there's stuff that keeps it in check, but not so in cultivation. My trick for small Utric specimens is to take the whole colony out of the water, change the water and scrub out anything on the container, then spray the Utric with water on an inclined surface like a large bowl. The algae falls away easily, leaving you with clean, more-or-less intact Utric stolons. It doesn't look quite as pristine as wild-grown colonies, I'm sure, but it's a good way to bulk up a small clump until it's big enough to take care of itself. If you use a container with peat or something as a substrate, you may want to skip cleaning the container and just do a water change, as I suppose you might get some beneficial critters living in there eventually.