What Does Good Flow Look Like?

There are three main functions of internal flow in your reef aquarium; keeping coral healthy, keeping fish healthy, and keeping the water healthy.  

  • Corals need flow to receive elements and nutrients/food but also to expel waste and byproducts.
  • Fish need flow to receive food, build muscle/exercise, and get oxygen. 
  • The water needs to flow in order to export fish waste and leftover food via filtration and for efficient gas exchange. 

As long as you are accomplishing all three of these functions successfully, you're doing it right. 

Why Is GPH A Bad Way To Shop?

GPH is a somewhat dated way to gauge a powerhead for internal flow because it's all about the type of flow and where that flow occurs. Furthermore, the way a particular powerhead manufacturer measures the GPH could vary based on the type of pump they are manufacturing. For example, 1000 GPH from a centrifugal pump will not accomplish the same thing as 1000 GPH from a wide flow, propeller style pump.

While we have attempted to adjust the GPH recommendations to account for modern propeller-style powerheads, it can still be quite misleading without a substantial amount of experience with all of the various pumps and powerheads on the market. When it comes to powerheads for internal flow, take the time to understand what your corals need, where you need that flow in the tank, and choose the pumps that can fulfill those needs. 

Where Are The Lowest Flow Areas Of The Tank?

The first step to eliminating dead spots in your tank is to identify where they are!  Here are some common areas of the tank where dead spots get created. 

  • Underneath a stream of laminar flow and directly below the pump
  • Behind or in between the rocks
  • Underneath or around large corals

As your corals grow, the dead spots are going to change because the growing corals will deflect and direct flow in your aquarium differently. You will need to move powerheads and/or add more powerheads to your aquarium as it matures. 

Flow Angle

The angle refers to the width of the flow pattern or the angles at which the stream of water exits the pump.  Some pumps shoot a very tight flow pattern which is equivalent to a narrow-angle flow pattern. Wide flow pumps have a much larger angle flow pattern. While most pump manufacturers don't give you an exact angle of the flow pattern, it certainly does matter because it can dictate where exactly you might use that particular pump. Typically a wide flow pattern will not travel as far as a narrow flow pattern pump. This information really goes a long way in the successful placement of powerheads in your tank.  


Velocity is how fast the water is moving. Wide flow patterns typically run at a lower velocity and the farther away from the pump you go, the lower the velocity of the water.  Narrow flow pumps maintain velocity for longer distances when compared to wide flow pumps.  Conversely, a wide flow pump will move a larger area or volume of water.  

Providing the right amount of flow is about understanding the relationship between the angle and velocity of the water flow so you can get the flow where it needs to be in your tank.  

Random Flow

While it has been debated, most modern reef tank owners will agree that providing varied flow patterns is indeed important for optimal health, especially among your coral. Varied or Random flow means the water will move at varying velocities and at different angles throughout the day. This is most often accomplished by adjusting or regulating pump speed. There are also special nozzles called random flow generators that help to randomize the flow coming from our return pumps.  Just how much should you vary the flow? That is typically based on the type of coral you are keeping


Turbulence can be defined as the erratic or chaotic movement of the water. Turbulence occurs in your tank where currents collide. This is most often accomplished by powerheads facing each other on opposite sides of the aquarium. The opposing streams of water will collide somewhere in the middle of the tank creating turbulence. It also happens when a stream of flow collides with a rock, tank wall, or the water's surface. Turbulence does matter because it can be very useful for creating varied flow patterns in your aquarium when utilized correctly. 

Current Streams

Current is a sustained stream of water flow that always moves in the same direction. It can be thought of as the opposite of turbulence. Creating currents can be very useful for moving long distances and around corals that do not handle turbulence all that well.


Yes, having the ability to aim the stream of water is very useful for targeting different areas of your tank. A pump that cannot be aimed means you're limited by the mounting location of the pump in terms of where that flow goes.  

Battery Backup

Every single aquarium will eventually go through some kind of power failure. Having just ONE PUMP that moves the water in your aquarium will sustain dissolved oxygen levels in the water and keep the tank's inhabitants alive during a power outage. Providing some kind of battery backup or generator to supply power during a failure can often be a matter of life and death in your tank.  

What Kind Of Flow Do My Corals Need?

  • Best For SPS: High-velocity, turbulent flow patterns. Corals that prefer high levels of PAR/Light will require higher amounts of flow.
  • Best For LPS: Medium-low velocity currents that are less turbulent but also varied throughout the day.  Provide both varied currents of flow with some time mild turbulence mixed in. 
  • Best For Soft Coral: Low velocity, very gentle currents that are varied throughout the day. Very wide flow patterns typically work best. Standing Wave motions like you get with a Tunze Wavebox is also very effective in this situation. 

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