How full does the pump need to be ina 5 Gallon fish tank?

We just got a new 5 Gallon fish tank and we will have maybe 3 to 4 Bettas possibly. How full dos the pump need to be?|||For a 5 gallon aquarium your air pump needs to be operated on full capacity in order to provide the maximum water agitation, create some water currents, and promote gas exchange.





Additional Note: If you are going to keep 3 or 4 Bettas in an aquarium, consider female Bettas because male Bettas are very territorial. My recommendation is that 3 Bettas are too much for a 5 gallon aquarium since they grow between 2"-3" inches long. Bettas love vegetation so you need to provide enough room to accommodate some plants.|||4 gallons|||5 gallons i believe needs 4|||Don't put 4 betta's in a 5 gallon.