Proper water flow is essential for removing waste, nutrient dispersal, and promoting the growth of corals and other marine life. Achieving the right flow, however, can be challenging because incorrect flow patterns can lead to dead spots, poor water quality, and unhealthy corals.

There are two primary methods of creating flow in a saltwater aquarium - using a return pump and powerheads. 

The Role of a Return Pump

A return pump is what moves water through the filtration and main display aquarium - its primary role is recirculation and ensuring the water comes in contact with your filtration at a sufficient pace. While not typically strong enough to provide the primary internal flow in a reef tank, a controllable return pump will at least contribute to creating a varied and turbulent flow pattern inside the display.  You can control the rate of flow to what is optimal for your filtration and, by default, will get some internal water movement as it flows back into the display.

Think of the return pump as the heart of your aquarium, it keeps the water moving to and from all of the critical components of your life support system. 

Utilizing Powerheads and Wavemakers

Powerheads, also known as wavemakers, are devices specifically designed to generate internal water movement inside the display aquarium to mimic natural ocean water movement. For the best results, it is important to consider three key factors when choosing a powerhead: flow rate, angle of flow, and shape of the flow.

  1. Flow Rate: The flow rate, measured in gallons or liters per hour, determines the strength of water movement. It is essential to select power heads with adequate flow rates to ensure sufficient water circulation in the aquarium.
  2. The angle of Flow: Finding the right angle of flow is crucial. Too narrow, and the flow may cause damage to corals; too wide, and the flow may dissipate too quickly, failing to provide adequate circulation. Researching and experimenting with different angles is necessary to achieve the desired flow pattern.
  3. The shape of the Flow: There are two main types of flow patterns—circular and laminar. Due to the aquarium's shape, a circular flow pattern is generally preferred. This pattern ensures that water is pushed across the entire tank, preventing dead spots and promoting proper water circulation.

This internal flow is most crucial for the health of corals because they have evolved on coral reefs - naturally very turbulent areas of the ocean. Within that, different corals come from different parts of the reef which dictates their preference for flow.  In general, we categorize corals as high, medium, and low-flow corals. Corals near the surface encounter lots of wave action that is very turbulent while corals near the middle and bottom of the reef encounter much gentler flow patterns.  SPS corals are, for the most part, high-flow corals.  LPS and soft corals make up the medium to low-flow corals.  

No matter how much flow they prefer, exposure to water flow is fundamental to the biology of coral and they will not survive without it. 

Tips for Optimizing Water Flow

  1. Place powerheads or wavemakers strategically: This is sometimes a game of chess because it's all based on the shape of your aquarium, rockwork, and coral placement. The most effective solutions will generate a circular flow pattern that moves water around the rocks.  Left front side and back right side pump positions can achieve such an effect. As corals grow, you may need to adjust the pump placement.  Powerheads should not be placed too close to the sand bed to avoid stirring up sand and avoid placement close to the water's surface because this can create suction noise and allow for air to whirlpool down into the pump.  
  2. Use multiple powerheads: Utilizing two or more powerheads positioned strategically can help achieve a consistent and well-distributed water flow pattern. Mirroring their placement on opposite sides of the tank helps create balanced circulation.
  3. Adjust power head settings: Experiment with different flow rates, pulse modes, and timing settings to find the ideal balance for your aquarium. Start with a moderate setting and make adjustments as needed, especially when introducing new corals or other marine life.
  4. Eliminate dead spots: Regularly monitor your tank for dead spots which are areas with insufficient flow because this is where debris and waste can accumulate. In addition to positioning your powerheads strategically, you can adjust the return nozzles from your return pump to redirect water and eliminate dead spots effectively.

Creating proper water flow in a saltwater aquarium is vital for maintaining water quality, promoting the health of corals, and preventing the accumulation of waste. By utilizing a combination of a controllable return pump and strategically placed power heads or wave makers, beginners can achieve an optimal flow pattern in their aquariums.