Bubbles can come from anywhere.. but if they are bubbles they will always be heading up. But if the white dots seem to head for the top of your tank its prolly bubbles. To get rid of bubbles I have a few sug.
1st. Make sure that your return bar is under syphon in your tank. This will keep from getting bubbles in your return bar. Try to purge the bar after your power the Pump back on.
2nd. Make sure that You dont have a skimmer output next to the return pump input. This will cause bubbles. Try moving the skimmer or retrofitting a "bubble cup" under the output of skimmer.
3rd. Make sure if you have LR that you spin it around to let all the bubbles out.
If Its not bubbles then youll have to repost and explain more.