What does this mean? (air bubbles)

What are you doing to new water before you put it in? What does your tap water test out like? Airstones, lowering water level to increase aeration, is all unnesisary IME, infact in some of my tanks the water surface is almost completely undisturbed.
 
Every time I put in new water I first use prime and let it sit for about 30 mintutes and then add it to the tank.

My tap water is:
pH: 7.6
nitrites & nitrate: 0
ammonia: 0.50

With the filter, I let the water flow like 2/8 of an inch from the top of the water surface.
 
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