Water circulation used to be something aquarists took for granted. If the filter was working, the water moved. Today we take water circulation much more seriously.
While a hang-on-back or canister filter may provide enough water circulation for a small tropical fish or goldfish tank, it isn’t enough for many marine, reef and planted aquariums. There are plenty of circulation and wave making pumps to choose from. But many aquarists wonder what’s the best way to aim these water pumps.
There is no “one size fits all” answer. Want to know why? We’ll look at why water circulation is important and how it affects different types of aquariums.
- Water flow in the freshwater planted aquarium
- Water flow in reef aquariums
- Final thoughts
Water flow in the freshwater planted aquarium
Most aquarists associate the need for water flow with reef aquariums.
But did you know aquatic plants need it too?
The underwater world is very different from the more familiar “dry land” environment we’re used to.
Water is more viscous and resistant to flow than air. Water requires more force to move it. Here’s an example.
The smoke from a candle wick is easily dispersed with a little puff of breath. Try blowing a drop of water across a flat surface. You have to huff and puff to get that droplet to move an inch!
So, what does this have to do with aquarium plants? Submerged aquatic plants rely on fluid movement to bring nutrients and carbon dioxide to their leaves. But there’s a catch called the “boundary layer”.
The boundary layer is a thin film of calm water that surrounds each leaf. The thickness of the boundary layer determines how easily nutrients, oxygen and carbon dioxide are exchanged between the leaf and the surrounding water.
A thick boundary layer will reduce the transfer of CO2 and essential nutrients into the plant, and release of oxygen into the water. Carbon dioxide diffuses 10,000 times more slowly in water than air.
So, it’s easy to see how plants can be stunted when this restrictive boundary layer coats the leaves in stagnate water.
How a circulation pump improves aquatic plant growth
Increasing water movement in the planted aquarium will improve plant growth.
Here’s why: water movement has long been recognized as a major factor influencing the growth and survival of submersed aquatic plants.
Biologists found that changes in water flow and velocity affects which plant species thrive in streams and rivers.
Studies have shown that photosynthesis rates of aquatic plants are positively correlated with moderate water flow rates. The same is true in our planted tanks.
Water moving across the plant leaves reduces the thickness of the boundary layer, making it easier for plants to obtain carbon dioxide and nutrients. Your plant’s growth rate can increase as much as six times when water flow is increased.
Too much flow can stunt aquatic plants
Its easy to assume that more flow is better, but this is not always true. You don’t need a big flow pump in a planted aquarium.
In fact, too much flow can actually reduce growth! Studies show that you only need mild water flow to maximize plant growth. A flow rate of about one inch per second produces the best plant growth.
When the flow is strong enough to twist and bend the leaves, plant growth slows down. Scientists think the physical stretching of high-velocity water movement stresses aquatic plants.
The key take away is you want gentle flow throughout the aquarium. There is no need to aggressive wave-like flow patterns. That is the problem created by ordinary power head pumps. The narrow, high-velocity output of powerheads creates an abrasive, damaging jet of water.
That’s why specialized circulation pumps are such a great way to increase water circulation without “power washing” your plants and fish.
Best placement of circulation pumps for planted aquariums
The ideal placement of the circulation pump will depend on the type and density of the plants.
If you’ve got thick stands of Vallisneria, position the pump so water penetrates the upright leaves. Wide leaf plants like swords benefit from a gentle flow.
But you don’t want the plants to be pushed over by the velocity. Experiment with different positions, watching how the plants bend, to find the best location. Many aquarists have success aiming the flow toward the glass.
The “bounce” effect dampens the flow and causes a general eddy-like pattern in the aquarium.
Avoid causing too much surface agitation. This will drive off carbon dioxide from the water, reducing availability to the plants.
Water flow in reef aquariums
Just like plants, corals develop a boundary layer around the coral polyps. Zooxanthellae algae living inside the coral tissue partner with the coral polyps to supply each other’s needs for food and nutrient recycling.
Since corals can’t move to where the best conditions are, they depend on water to bring food and essential elements for many biologically necessary processes.
These processes include photosynthesis by zooxanthellae, carbonate skeleton building, reproduction, and nutrient and dissolved gas exchange. In nature, corals are typically found in shallow coastal reefs.
Water motion is created by both currents and wave action. These two types of circulation bathe the corals with clean water, flushing away waste products, preventing sedimentation on the corals, and brings a steady supply of plankton and essential nutrients to the polyps.
How water circulation improves coral health and growth
Our reef tanks are miniature ecosystems designed to reproduce, as close as possible, the environmental conditions required by corals and other reef organisms. We know corals and reef rock are exposed to steady currents and cyclic wave action.
After years of experimentation, we’ve finally developed specialized water pumps than can recreate the many reef water flow patterns required for corals to thrive. Here’s the science behind corals and water movement in reef tanks.
Just relying on the filter’s output won’t adequately “stir” a reef aquarium. The rockwork, shape of the tank and even the coral frags redirect and inhibit currents inside the aquarium. Corals have about a 1-mm layer of stagnant water around their polyps and tissue.
Water movement is needed to constantly prevent this boundary layer from growing due to inadequate water flow. If not, the coral animals and their internal symbiotic algae won’t get the nutrients (phosphate and ammonia) they need or have efficient exchange of carbon dioxide and oxygen at the tissue level.
This causes a “bottleneck” in the flow of energy to the coral. The waving and pumping of polyps will help, but its not enough to counter the negative effects of slow-moving aquarium water. Adding wave or circulation pumps eliminates this problem.
Through thousands of real-world experiments, home aquarists and public aquariums have witnessed the benefits of wave action when keeping corals in the aquarium. Here’s what you’ll see with proper water flow:
Best placement of circulation pumps in reef aquariums
Since no two reef aquariums are the same, there are no set rules on how to configure circulation pumps in your reef tank. But that’s what makes reef-keeping fun! Hands-on experimentation. Here’s what you need to consider when setting up your circulation pumps.
There are single-speed pumps that are basically “point and shoot”. Mount the pump on the glass and experiment with aiming the pump. The circulation pattern is influenced by the rockwork and size of the aquarium.
A nano reef is easy. You’ll only need to aim one small nano wave pump to get the job done. Larger tanks will benefit from several small pumps or one larger wave pump. You can aim directly at corals if the pump is not too powerful. Try bouncing the flow off a glass wall to create a high-volume current.
You may want to think about using a “smart” circulation pump. These can be controlled with a wired controller or wirelessly through a phone or computer. These circulation pumps have built-in programs that automatically create flow patterns like wave surges, slack tides, gyre patterns and more. The other benefit of smart pumps is that you can control the pump speed and duration.
Here’s a practical example.
You probably don’t want to blast your corals with water all day and night. It isn’t natural or beneficial. But you can set the pump’s program to periodically hit the reef tank with wave surges. With experimentation, you’ll find the sweet spot to aim the pumps so the surge flushes the rockwork and corals, sending debris into the filter.
To slow the flow at feeding time, just hit the “feeding mode”, putting the pump into a temporary low-flow mode. This is helpful when you’ve aimed the pump for high-velocity surges but want a quite period to feed the fish and corals. This prevents most of the food from getting pulled into the filter.
Water flow is important in all aquariums. Even if you don’t have a reef tank or planted aquarium, dead spots make it easy for debris to collect and form sludge.
You’ll find most circulation pumps are marketed with reef-keepers in mind, but don’t let that deter you from using them on a freshwater tank.
These high-tech circulation pumps come in a variety of sizes that will work in any size aquarium. The key to getting the best results is proper aiming.
Take your time and have fun experimenting with aiming and pump placements. You’ll see the benefits to your aquarium immediately!