This is what I've been using for my four-bed system. I don't know what it's limitations are but I think it's well beyond four beds.

Simple Deluxe Air Pump 18-58W 602/1030/1189 GPH 38-75L/Min With Adjustable Air Flow Outlets For Aquarium, Pond, Hydroponics Systems, Silver https://a.co/d/epLfCE2