I've just recently noticed small 1/8 to 3/16 inch bubbles coming up from my live sand bed. The bed is only 1" deep and has very little algae on it. When the hermit crabs scavenge over the bed bubbles come up every 1/2 inch of their travel. Bubbles come out of the sand randomly even when nothing is walking over the substrate. Seems to be only one or two bubbles at any one time being leased over the 4 foot tank floor.
I have searched the reason for this and the points I've come across are;

Trapped air in sand bed. Yes months ago I did introduce the sand into a filled tank but why would it take so long for the air to escape.

Nitrogen gas escaping due to the BB doing their job on nitrates in the tank. Maybe, my nitrate readings have been 0ppm (liquid API test kit), for a long period of time. Check yesterday and no nitrates present according to my test tube.

So then I came across two conflicting points;
1. Stir the sand to release the bubbles.

2. Don't stir the sand, let the bubbles release on their own.

Advise please. Thanks in advance.