Air Pump Question?

[growGuRoo]

I have a 4 three gallon bucket DWC setup. With an ancient air pump. (whisper 9000). Its at least 15 years old and dying. I'm not sure how air pumps are measured. GPH?
I would like to put two 4" air stones in each bucket. What pump should i be purchasing? Not looking to buy "fish tank" pumps either.

 

[JJ Bones]

Measures it by Gallons Per Air per Hour which is a way to measure how strong of a pump you need; depending how much water you're aerating.

I personally like the Sunleaves Durapump Air series.