I have a glass jug with some water spinach growing in it, and lots of quite small critters swirling around. I looked with a jewelers loop, they do not like daphnia so far as I can tell, but sort of semi-circular, like a very tiny beetle. Though water beetles are big. There are a few mosquito larvae in there, but I have put in some bt israelensis, that should kill them shortly. I guesstimate they are about 1/4 the size of a pencil tip. There is also a small reed in there, maybe they came with it. Any ideas what these little devils might be, and might they be of interest to you?