The way im looking at it specifically is if the tank is big and you have the powerhead under 2" or more water it may not be enough agitation even with the vent on.
With the appropriate size air pump you could airate the tank at a faster rate, the picture i took is in a 75gal 4feet wide. The bubbles reach about 2 feet out in front of the powerhead.
So about 3" wide and 2 feet long agitation on the surface vs maybe 4"x4" from a breeder sponge or air stone.
Going on the assumption that you already have an air pump and a powerhead. Wouldnt this allow you to further airate your tank with the same equipment?
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