You will need a good size filter to manage a 30 gallons tank. It should have a flow rate of 130-150 gallons per hour. Similarly, if you have a 30 gallons tank inbuilt in your aquarium, then you will need the filter that should have a GPH rate of 90-120. Alternatively, the reef tank of 30 gallons will need a canister filter of 150-195 GPH.