All 3 are synonymous: impellers with a lot of thin blades. A standard impeller (in this hobby) has about 4-6 'paddles', while a 'neeedle wheel' might have x3-x4 that number.
Commonly used to chop up co2 for better diffusion. A needle impeller that rotates at a slower RPM then a 'regular' impeller is better suited for that purpose.
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