I just noticed my ten gallon tank I've been running has these VERY tiny, small white things that seem to dart in order to move. I tried taking a photo but they are so small my camera can't focus on them. I read a few other forum posts after googling that they be copepods but I'm not sure. The only change I've mad was a recent addition of an amazon sword I bought at petsmart. I'd find it difficult to believe they came from it, however, because I only buy the plants in the tubes and have NEVER had any "hitchhikers" from these plants before.