Don’t Let the Water Flow Slow in Your Marine Aquarium

water-flowWe’ve mentioned several times here at Saltwater Smarts how the output of reef aquarium lighting gradually and imperceptibly shifts away from the desired level over time. But did you know a very similar phenomenon can occur with the rate of water flow in your aquarium system?

That’s right! If certain simple steps aren’t taken on a routine basis, your aquarium’s water flow can very gradually slow to a crawl, leading to a variety of ill effects for your system and livestock. For example:

  • Instead of remaining suspended in the water column where they can be filtered out, fish waste, uneaten food, and other organic particulate matter will tend to settle onto the rocks and substrate where they’ll decompose, promoting excess dissolved nutrients and detritus buildup in the process.
  • Gas exchange will be reduced, decreasing the level of dissolved oxygen in the system.
  • With no strong current to carry off their wastes and prevent detritus from settling on their tissues, the health of corals and other sessile invertebrates may suffer.
  • Fish that are enticed to eat only when food is in motion and shy/site-attached fish that depend on the current to deliver food right to their “front door” (such as jawfishes) may either lose interest in feeding or find that meals are always just out of reach.
  • Cyanobacteria, which favors areas of low flow coupled with excess dissolved nutrients, will be more likely to flourish.

So what can you do to keep the flow going strong in your aquarium? Essentially, it comes down to routinely cleaning and maintaining the following components:

Sump return pumps and powerheads

Think of these pumps as the heart of your system—they keep the “life blood” flowing. But they also have a tendency to get clogged up over time, which reduces their output. Pump intakes can become obstructed by hair algae, bubble algae, and other floating debris. Slotted housings can be virtually cemented shut with coralline algae left to its own devices. Of course, the insides of these pumps can become gummed up with all manner of gunk and even various sessile life forms, such as those ubiquitous (and very sharp) vermetid snails.

On at least a bimonthly basis, it’s a good idea to disassemble each submersible pump; brush away any debris, gunk, or attached vermetids from all the components; and then soak the components in white vinegar for a few hours to dissolve coralline concretions before rinsing and reassembling the pump.

Pump return nozzles

Nozzles that discharge water back into the display tank from sump pumps or canister-style filters seem to attract hair algae like moths to a flame. As the algae builds up around and inside the nozzle opening, the flow of its effluent can slow. Also, these nozzles may have a small hole in them at or just above the water line, which is designed to break the siphon and prevent the backflow of water in the event of a power outage. This hole can easily become clogged with calcium deposits, coralline algae, or hair algae.

About once a week (during every water change), I give the return nozzles in my tanks a good going over with an old toothbrush to make sure they’re completely unobstructed and flowing properly. They also benefit from an occasional soaking in white vinegar.

Pipes and hoses

If pumps are the heart of a marine aquarium’s “circulatory system,” the pipes and hoses attached to them are the veins and arteries. And just like our blood vessels, they can become clogged over time (especially transparent hoses exposed to sunlight)—though usually with slimy, brown gunk, not cholesterol plaques.

For obvious reasons, cleaning the inside surfaces of pipes and hoses can be a bit tricky. For the most part, you do what you can to get inside there with a long-handled aquarium brush. There are also magnetic hose-cleaning brushes on the market that can do the job—they pretty much operate on the same principle as algae magnets used to clean the inside panes of an aquarium, though the cleaning brush is much smaller.

To clean flexible hoses, which I do approximately bimonthly or as needed, I simply tie an aquarium brush of the appropriate diameter to a length of sturdy twine, feed the twine through the hose until it emerges at the opposite end, and then pull the brush through. Repeat this a few times and rinse, and your hoses will clean up nicely.

Overflow chambers and standpipes

Overflow chambers and standpipe openings are also prone to getting clogged with hair algae, coralline algae, vermetids, and other gunk. These should be brushed/scraped clean on a weekly to biweekly basis. Pay special attention to the slots of an overflow, as these commonly become narrowed with algal growth. Brush each slot individually. Also, if your overflow includes one of those U-shaped siphon tubes, be sure to run a brush through it as well. Of course, white vinegar can be brought to bear on any overflow components that are encrusted with coralline, vermetids, or calcium deposits.

Mechanical filtration media

Last but not least, pay attention to the state of any mechanical filtration media. As they do their job of trapping particulate waste, filter socks, foam blocks, sponge sleeves, bonded filter pads, etc., become clogged. Be sure to rinse them frequently and replace them periodically so they don’t become an impediment to water flow.


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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. I have a 48l nano with a trickle filter and a 900lph power head and my tank is getting covered in cyno I feed my one yellow tail damsel once a day using a small syringe. I can not get rid of it or know why it has happened any ideas

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