Air holes in avocado when filling tank

[rcalvy1]

hi guys,
I'm getting hair pockets in my tank when filling it. Here's a pic, any reason why this is happening? Thanks

 

[Jim_ MDP]

Surface tension... the inverse of filling a glass above the rim.
Get a toothpick and pop it.

LOL... haven't a clue, I don't own one.
And I'm not sure what the air pocket is doing that's "wrong".

Shake it.