Saltwater Aquarium Blog

Why It’s Important in a Saltwater Aquarium

Maintaining high-quality saltwater is, arguably, the most important thing you do for your reef aquarium. And I bet if I asked for the most important water parameters, you’d list temperature, pH, and nutrient or contaminant levels. Well, one other important water parameter often gets ignored, neglected, or otherwise taken for granted: water movement. Your water flow throughout the tank is crucial for maintaining the health of everything living in the aquarium – from the bacteria up to your favorite fish. Yet it’s often overlooked on the checklist when setting up a new saltwater aquarium. Good thing you’re here to learn why it’s so essential to keep water flowing through your tank!

Table of Contents: Water Movement

Fish and invertebrates in the ocean enjoy the benefits of currents and tides. The ebb and flow of these natural phenomena create a constant state of water movement within their environment. It’s something they’ve adapted to. And you should replicate that system in your smaller tank ecosystem. But do you know everything those currents provide? Or why water flow is such a vital part of the ocean (to say nothing of your aquarium)? That’s where the following links come in handy. Feel free to pick any of the topics that catch your attention. Or stick around through the entire article to learn why it’s best to invest in quality powerheads for your favorite tank.

Aquarium powerheads aid in water movement

Water Movement in a Saltwater Aquarium

If you’re like me, you thought about water movement when you first set up your tank – and then promptly forgot about this part of aquarium management. But water flow is critically important to water quality. And whether you’re planning to set up a new saltwater aquarium or have an existing tank, it’s worth taking a closer look at the current within your tank. The type, direction, and velocity of the current in a saltwater aquarium are some of the most critical environmental variables determining the long-term health of the inhabitants in your tank. We’re talking right up there with temperature, pH, and chemical composition.

Why? Because pushing water around with a powerhead simulates the currents and tides of the ocean. And that water movement accomplishes the exact tasks those natural processes do in the wild:

  • Facilitates gas exchange
  • Food delivery
  • Waste management
  • Prevention of “dead zone” development

Those four critical tasks help balance the work you attempt to do when you look at your water parameters. And if you’re NOT attempting to get some kind of water flow happening, you’ll find yourself with a stagnant pond. (A saltwater pond, but a pond all the same) Happened upon one before? They’re not beautiful. Nor do they contain healthy, thriving communities of fish and invertebrates. (Algae, yes. But who wants a tank full of disgusting algae?)

This is where water movement comes in. But let’s break down each of those critical tasks, shall we? Then you can see WHY you need to take care of your powerheads – and pay attention to where you set them and how you adjust the settings.

Gas Exchange

Everything living breathes. (Hopefully, you already knew that) While they survive underwater, corals and fish still need to take in oxygen and exhale carbon dioxide – in some way, shape, or form. (Yes, I know, corals use their zooxanthellae and photosynthesis – which is the opposite process. Stay with me here) Any time you trade one for the other, it’s gas exchange. The official exchange takes place in the lungs or across membranes. But without water movement, the process becomes complicated.

Think about it: Say you’re in a closed room with no vents, windows, or openings of any kind. You still have air to breathe, of course, but over time, it turns stale. And the amount of oxygen decreases. You’re not getting ventilation to clear your exhaled air away. No wind, either, to freshen things. Stay there long enough, and your lungs WILL struggle to pull enough oxygen into your system. It’s the same for a fish or coral in an aquarium with no water movement.

Coral need water movement for gas exchange

Powerheads keep a current bouncing around the tank walls. The flow sweeps carbon dioxide away, swirls it up to the surface, and releases it from the aquarium. Then oxygen gets collected, and the fish and invertebrates can take in the “fresh air.” Your water movement acts as the wind in the system. It’s the current moving around and preventing “stale air” from hanging around. So everyone breathes easier.

Handy, considering you don’t find tanks with windows or vents.

Food Delivery

Corals don’t move. Sure, their tentacles wave around, but the skeleton keeps the main body firmly in place. You may have other sessile invertebrates in your aquarium that prefer to adopt the couch potato lifestyle. And then you’ll find burrowing fish and invertebrates that do nothing more than poke their heads out of the sand. They’d rather their meals come to them. (Going out for “take out” isn’t their style) Sounds lazy, but it’s an adaptation that works perfectly in the wild. But it works because of currents – or water movement.

Jawfish depend on water movement for food delivery

You want your aquarium to act as a mini, NATURAL ecosystem. And that means allowing your corals and fish to behave the way they would in the ocean. Finding the proper water flow that delivers plankton and other tasty morsels to these creatures facilitates those feeding behaviors. With a refugium, you can grow pods or other microfauna in a safe space. As the colony flourishes, it slips into the current created by your powerhead. And the water movement delivers an easy meal.

You’re creating a food delivery system that mimics the one these animals enjoy in their native environment. (Minus a tip)

Waste Management

Now, you’ve fed your fish and invertebrates. That means nature will run its course and produce waste. Where I work, we commonly say “stuff” rolls downhill. It’s intended for other things, but in the saltwater aquarium hobby, the phrase works literally. Waste falls to the bottom of the tank. And without water movement? That’s where it tends to stay. (Yes, even if you keep up with a regular cleaning schedule)

However, when you have water flow at work, you create a waste management system. As your current’s constantly pushing things into motion, the waste, leftover food, and other detritus remain suspended in the water column. Flow gives the system a better chance of moving everything into your filters to scrub the unwanted mess OUT of the water instead of collecting on the substrate. This means a cleaner, healthier tank. All from a bit of water movement. (Okay, so it’s probably more than a LITTLE, but you get the idea)

If you don’t believe me, try this experiment: Add some sand to a jar and let it set. Now try shaking it or swirling it around. That movement agitates things and keeps the sand up where a skimmer or filter intake has the chance to reach it. No movement, though? Yeah, the waste will sit there until you break out the vacuum. And manual cleanings pose a greater chance of stressing your fish than water movement – something they WANT.

Avoidance of Dead Zones

Dead zones crop up in aquariums without water movement. They’re pockets that lack ALL of the above. As such, they allow problem algae to gain a foothold and thrive. Algae, while alive, doesn’t have a problem enduring less-than-ideal conditions. (Remember that stagnant pond? You always see algae choking such places) Without a current to sweep away wastes – a tasty resource for these organisms – or bring in fresh gas exchange, you create dead zones.

Except they’re anything BUT dead!

In the ocean, surges of “nutrients” (usually from run-off) lead to algae blooms. Red tides herald problem areas – and they’re deadly to the natural flora and fauna in the area. You won’t have the “tide” part in your tank, but you can see the same overgrowth of unwanted algae. All from the lack of water movement.

Red tides result from nutrient surges in the ocean

It’s better to have a current sweeping through your tank to prevent these pockets from developing. It won’t STOP algae from growing, but it’ll help eliminate dead zones. (Yes, it sounds cool to say you have a dead zone in your aquarium. However, dealing with the reality of one isn’t as cool)

Understanding Water Movement in an Aquarium

On board with water movement for your saltwater aquarium? Excellent! Unfortunately, there are a few caveats to adding a current. Because not every setting on your powerhead will work. You need to understand how things work in the confines of a tank. Otherwise, you could cause more problems than you solve.

Turbulent vs. Laminar Flow

Water movement on coral reefs is usually characterized as turbulent. This means it’s a chaotic, non-predictable flow pattern. (If you need to, think of airplane turbulence, when winds collide in a storm, leading to instability) The flow comes from multiple sources:

  • Underwater currents
  • Wind
  • Wave action
  • Tides

All of these forces converge and create the vibrant, life-sustaining flow of the coral reef. Turbulent flow checks all of the boxes of water movement that we just went over.

Then you have the water movement created by most pumps or powerheads. It’s known as laminar flow. Laminar flow is water that moves in a straight line. Most aquarium pumps or powerheads suck water in from one side and spit it out the other. You get SOME turbulence as the water strikes the tank walls and bounces back, but not to the degree you see in the ocean.

So how you are supposed to create turbulent flow when your equipment conspires against you? With a little work.

Using Powerheads to Create Water Movement

Turbulent flow depends on obstacles to generate that chaotic pattern. And one of the easiest things you can do in your aquarium is point two or more pumps at an angle, so the flow of water from each crashes into the other. Bingo! Instant turbulence. Or you can aim the water movement towards an obstruction like a piece of live rock. You’ll create the same turbulent flow that way. (It mimics the current crashing into the reef)

You also have the option of setting your pumps on a timer. Turn them on and off in a sequence to create a more pulsatile (and less regular) flow. You’ll disrupt that laminar pattern while still generating water movement throughout the tank. Not to mention creating more realistic conditions for your fish and invertebrates. (It’s that “chaos” part of the turbulence equation)

Finally, you can add a wavemaker or surge device to complement the water flow created by your pumps or powerheads. Not only will this mimic the natural patterns of the ocean, but it’ll also boost that gas exchange you’re looking for. It’s something to consider if you have room in your budget.

Or, you know, you can do ALL of these things and really set up a mini-ecosystem!

Setting your powerheads at different angles or levels will create water movement

Cautions with Powerheads

Of course, everything comes with a price. Changes in water movement CAN hurt the animals in your saltwater aquarium. Species live in different parts of a reef, where they experience different ranges of current. And they’re adapted to those water flows. If they experience a sudden change, it can lead to stress. And it doesn’t take much to provoke a change.

Intake sponges become clogged. Powerheads get jammed by snail shells (with or without the snail attached). Suddenly, the water movement in your tank gets altered. And your corals and sessile or burrowing creatures suffer. I even had a powerhead DETACH from an aquarium wall, redirecting its flow and destroying a prized LPS coral!

Fish and corals acclimate to the pattern of water flow you set up in your tank. It’s the same process they undergo with the other water parameter. Changes from a less desirable flow pattern to a long-term, more desirable water movement pattern can lead to stress. It may be short-term, but you need to take that into account. Acclimate your organisms as delicately as possible whenever you make changes to the current in your tank.

Finally, check the efficiency of the pumps you’re using. The costs to run powerheads can vary dramatically based on the model pumps you choose. You want to keep your system healthy and running smooth, but not at the cost of your electric bill. Do your homework and find a brand and model that won’t break your bank.

For More Information

Water movement is often overlooked and demoted in hobbyists’ minds. But that current plays a crucial role in your saltwater aquarium. You want to mimic the natural habitat of your fish and invertebrates as closely as possible. But you also want your tank to remain healthy. A few powerheads – or a wavemaker thrown in – can do wonders for both. And if you need a little more convincing? This bonus information should do the trick.

Let’s start with a YouTube video on water movement – complete with a guide on pumps and powerheads:

Have you ever been to the Great Barrier Reef? Dive into this immersive, interactive underwater display  (Don’t worry – it’s free!). You’ll see water movement, in the form of turbulent flow, at work!

And if you’re interested in some of those burrowing animals that would LOVE a food delivery service, got you covered:

Written by Albert B. Ulrich III, author of The Reef Aquarium Series of books:  The New Saltwater Aquarium Guide, How to Frag Corals, and 107 Tips for the Marine Reef Aquarium.

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