Pic is a little too blurry for me to make these out but I would hazard a guess at two possible suspects -
Do these little dots move, circular and looks like has tiny wings on back and flicks about rather quickly?
If so, then it sounds like could be copepods, basically tiny little crustaceans. Fish will happy snack on these, pretty harmless really.
OR if they are like tiny little whitish worms, moves/wriggles fairly slowly?
Then likely to be a planarian type worms. Mostly harmless but there are some species that do a bit more harm than good to snails and shrimps. But again, most fish will happily eat these.