is that that string form of algae????!!!I would advise you remove those moss balls asap! Soon you will find your plants with tufts of cladophora algae release by the moss balls. Cladophora is very tough to remove on plant leaves once it gets a hold. I know your shrimp love them (great for food) but its not worth the hassle.
I have a bunch of moss balls in my sump so my fry and shrimp can feed off them. They also help reduce other forms of algae as well as nutrient uptake. So they are not all bad, but they will shed algae on to your other plants.
ihad my moss ball in my 20 l and inotced this green string algae growing on my plants iwas like WTH