If you are referring to the strands in the top/centre of the photos with little "lumps" along them, it is Bladderwort. Some people think of this as algae, but it is a true plant, in the genus Utricularia. There is another thread about this from the past week or two, though I can't remember what was posted in it.
I rather like this plant; I had it suddenly appear in two of my tanks, up among the floating plants. Thought at first it was a string or hair algae, but then learned what is actually is. It can make quite a lovely floating plant. They flower, though I've not had this occur.
They are carnivorous, which is probably why some aquarists dislike them. Not something you want in fry tanks, because while they might or might not eat very small fry, they do eat daphnia and infusoria, a prime food source for fry. And of course, moss is the ideal "home" for such small critters, so it is not surprising the bladderwort appears there. The genus name comes from the "utricles" which are bladder-like organs (hence the common name) that are hollow chambers that can sense prey and then open to suck it in, so to speak.
Byron.