Well first is your water level up to the black rim on the tank ( that is you have a regular glass aquarium) if not the water is dropping realy down a few inches and creating tiny air bubbles but that only occurs if you have a hang on back filter. Also do you have any type of aerator in your tank that is close to the part of the filter where it sucks in water because if you do it could be sucking up air bubbles which will cuase the pump in the filter to cavitate and chop the air bubbles into millions of smaller ones and then they come out into the tank where you can see have as much.
10 gallon salt water 3 damsels
20 saltwater mini reek yellow tang green mandrin goby, clownfish, yellowtail damsel, coral banded shrimp, skunk cleaner shrimp, lots of corals and fiji rock
75 gallon cycling soon to be reef tank