Unknown bug

Question
Very small round, needle/pinhead size, bugs crawling and swimming in freshwater aquarium. Do you know what these are? I really need to find out.

Answer
John,
Do they look like worms crawling on the glass? What color are they? Are they all over the tank? Swimming on the top of the water or all around? I need as much information as you can give me. Usually, small bugs in the water are due to bad water conditions. What size tank is it and what kind of fish?