If it is extremely tiny then it is probably a chigger.
It's called a pseudo-scorpion. See what they look like by entering the term on Google Images, they are fascinating little creatures.
Without a proper description it is impossble to say what they are. If they really are bugs and they worry you, it may be a good idea to take the filter out and give it a scrub.
It might be a Chigger. See http://en.wikipedia.org/wiki/Chiggers
It is most likely to be a jitterbug, if you are in the north of the united states in states like Michigan Ohio etc.