I like to occasionally put some air into the tadpole containers. Sadly the aquarium pump from eons ago was either thrown out, given away, or lost.  What I've done in the past was do it manually with a straw but with the current group being so young/small I wanted something "less violent."  The solution was simple: cram some paper towel on the end that goes into the water to reduce the opening size on the end of the straw and thus produce smaller bubbles. Before and after videos show below: