5 Signs of Inadequate Water Movement in Reef Aquariums

Powerheads are used to boost the overall flow in an aquariumProper water circulation is one of many elements that are key to maintaining a healthy reef system. While there’s no such thing as a one-size-fits-all water-flow scheme (you really have to tailor the flow to the unique needs of the invertebrates you keep), there are certain signs that will tip you off to inadequate circulation. Among them:

1) Detritus buildup in “dead spots”

Some settling of detritus is unavoidable in a reef system, but excessive buildup tends to occur in tanks with inadequate water movement or “dead spots”—specific areas in the tank with poor to nonexistent flow. A good level of water movement will keep most particulate matter in suspension long enough to be captured by mechanical filtration media (socks, sponges, etc.), so this is a sign that you need to either boost the overall flow in the tank, by adding more or stronger sources (e.g. powerheads), or redirect existing water-flow sources to greater effect.

2) Corals fail to expand

When coral specimens remain in a prolonged contracted state—with their tissues/polyps withdrawn—one possible explanation is inadequate water movement. Now, many different environmental factors can cause this behavior, so failure to expand is by no means diagnostic, but that symptom coupled with others listed here may be a good indicator that better circulation is in order.

3) Leather corals have trouble shedding

Along very similar lines, if your livestock includes leather corals (e.g., Sarcophyton and Sinularia spp.), which occasionally go through a natural process of contracting their polyps, developing a waxy coating over their surface, and then eventually sloughing off this layer, inadequate water flow may make it difficult for them to shed. Or, they may go in and out of this cycle more frequently than seems normal.

4) Cyano shows up

Cyanobacteria, which tends to grow in loosely attached patches and mats, favors areas of slack water movement, so it’s appearance often indicates insufficient water flow overall or the presence of dead spots. Of course, cyano also favors elevated dissolved pollutant levels, so if it develops in your tank, you have more than one problem to remedy.

5) An “oil slick” on the surface

The buildup of an oily film on the water surface is a clear indicator of insufficient water movement. A little roiling action at the water surface (e.g., created by powerheads and/or sump returns positioned just below the surface) coupled with good protein skimming will help prevent this buildup while promoting good gas exchange in the system.

What symptoms have I missed?
What other signs and symptoms of inadequate reef system water flow can you think of? Please share them with your fellow salties in the comment section below.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. Great information another good indicator is not just cyanobacteria but other nuisance algae will firm in low flow areas. I remember one of my first tanks had a dead spot and algae only grew in that location. So I agree water movement especially for gas exchange is very important part of a healthy reef system.

    • So true, Jon! Not to mention, it can sometimes be tough to completely eliminate all those dead spots depending on aquascaping, coral growth habit, and other factors.

  2. Another great article guys…!
    I too, had the low flow syndrome and ran out and accumulated a few bargain priced powerheads. After losing fish, after fish and every tang I purchased and banging my head against the wall during many sleepless nights wondering Why..I realized those cheap powerheads were in fact adding an amazing amounts of STRAY VOLTAGE…in reality, 30 volts worth…basically cooking my fish with electric current.
    I now have my tank down to .30volts !
    Does anyone recommend a few Great choices of no voltage giving powerheads. I have since acquired a mp40 ecotech. Love it..

    • Thanks for your comments, Jim. With respect to eliminating the potential for stray voltage, I think you’re definitely on the right track using EcoTech pumps or others that have their electronic components outside the tank (if there are any other brands with that same feature). Any other salties have a different suggestion?

  3. I broke down and bought 2 Vortech mp40’s all else failed to control algae and cyano, I still have cyano. My hair algea has finally subsided but the cyano creeps back. I don’t think I have the flow correct and can’t find any info on the ideal flow (pattern?). I turned up the flow yesterday and today found a large piece of live rock toppled over. I guess I turned it up too high!. It also seems my overflow box is in the way, high flow makes a lot splashy water noise. I’ll take any suggestions.

    • Jeff Kurtz says

      Hi Kathy! Generally speaking, the type of flow you’re looking for is turbulent and non-linear–in other words, you don’t want to blast your invertebrates with a jet of continuous straight-line current (e.g., directing the effluent of an impeller-type powerhead directly at a coral). Rather, the water should flow at them in a random, omnidirectional fashion. Of course, as mentioned in the post, the intensity of the water movement must match the unique needs of the species you’re keeping.

      With respect to your cyano problem, don’t forget that slack water movement is just one factor that contributes to cyano growth. An excess of dissolved nutrients is usually the underlying problem, so moderate stocking/feeding, copious water changes with purified source water, and robust protein skimming are going to be your biggest allies here. Can you give us a little more information on those aspects of your system? That might help us zero in on the source of your problem.

  4. I don’t think some people know the massive amount of water movement there are in some places. In the Caymans for instance there are places where you can’t even swim, all you can do is sit back and let the current take you because you would never be able to fight it. The sea fans in those places are very numerous and you can practically hear them sing they are vibrating so fast. That is also the reason we have a very hard time keeping them in a tank. In the South Pacific I have seen shores that are constantly pounded by the surf and just below the surface is carpeted with corals. You would think they would get a head ache, if they had a head of course. It always amazes me that there are so many fish in those places and they don’t get smashed into the rocks.

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