Micro Bubbles

Where are they coming from? Skimmer? Powerhead sucking in air? Bubbles from the sump?

 

That's really odd. I know my maxi-modded MJ1200's suck in air sometimes if I don't set the shield right. How deep is your sand bed? Could you be getting bubbles from decaying material in the bed getting sucked into your powerhead? Are you sure they're bubbles and not a bacteria bloom or undissolved calcium or some supplement you put in the water?

 

Put some filter floss near your return pump and those will usually eat up most of the micro bubbles. Atleast that has always worked for me. What type of nano are you running again?

 

if your not getting bubbles through the filter replace your hose it pry has a hole or use a plastic clip hose clamp. you have a small gap somewhere in the return line sucking in air,some customers have had it happen on their bio cubes

 

I'll bet ya a dollar your problem lies in the hose, or a loose connection.