The Minimal Role of Mechanical Filtration in Marine Aquariums

Powered mechanical filters play a lessened role for saltwater aquariums compared to freshwater

Powered mechanical filters play a lessened role for saltwater aquariums compared to freshwater

Mechanical filtration—the physical straining out of suspended particulates from aquarium water—has something of a mixed reputation among marine aquarium hobbyists.

This may seem odd to those with experience in the freshwater side of the hobby, where the use of hang-on-back and canister power filters is quite commonplace. But then, freshwater fishkeepers tend to think of us salties as a rather peculiar bunch in general—something Chris and I probably should have warned you about before we attempted to seduce you into joining the dark . . . er, I mean the saltwater side of the hobby.

But now that you’re one of us and there’s no turning back, let’s explore the role mechanical filtration plays in marine aquariums.

Why the dubious reputation?

The issue with using dedicated mechanical filters on a regular basis in saltwater systems, where exceptional water quality is non-negotiable, is that they tend to do their job of trapping suspended particulate waste too well. All that trapped gunk—which is merely sequestered within the system, not removed from it—tends to decompose rapidly, so if you don’t clean the filter frequently enough (which is very often the case because “out of sight means out of mind”), the dissolved nutrient level in the system will soon begin to climb.

Also, the media used in mechanical filters can easily become biologically active—i.e., colonized with nitrifying bacteria—if not rinsed or replaced often enough. Then, when you finally get around to cleaning or replacing the medium, you’ll essentially lose a portion of your biofilter.

Many reefkeepers tend to shy away from mechanical filtration not just for these reasons, but also because mechanical filters can trap good particulates along with the bad—including planktonic microfauna that they might want in their tank as invertebrate food.

So how do they keep the water clean?

Most marine aquarium hobbyists strive to maintain excellent water quality through vigorous protein skimming and frequent partial water changes. But despite this de-emphasis on mechanical filtration, many saltwater hobbyists still utilize at least some form of it.

For instance, mesh filter socks, sponge sleeves, foam blocks, and bonded filter pads are often placed in various locations within a marine aquarium’s “circulatory system” to trap particulate waste. Of course, these, too, must be rinsed or replaced frequently to prevent them from becoming biologically active and/or a repository for decomposing gunk. But it’s usually easy to do so because they’re plainly visible and you don’t have to tear down any equipment to access them.

Power filters still have a place!

Before anyone gets the idea that I’m knocking powered mechanical filters, let me assure you that they can still play an important role in maintaining good water quality in a marine system—just on more of a part-time basis.

A hang-on-back or canister filter is a great tool for those occasional heavier cleanups. For instance, if you kick up a lot of detritus during routine maintenance or when stirring the surface of your sand bed, you can temporarily hook up a mechanical filter to help eliminate this suspended debris. Similarly, if you want to “polish” your water a bit, you can always temporarily set up a power filter with activated carbon in the chamber.

I’ve used a hang-on-back filter combined with frequent water changes as part of my quarantine protocol for many years. Sometimes it takes a lot of experimentation with different foods to get a finicky new specimen to eat, and the power filter saves me a lot of trouble siphoning out uneaten food.

What’s your preference?
So, fellow salties, what’s your take on mechanical filtration in marine systems? Are you pro or con? Any interesting anecdotes to share? Let us know 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. I have a fluval 70 aqua clear for my 37 gal saltwater tank. That and marineland 400 powerhead are the only filtration in the tank. Haven’t had any real problems at all. Have 20 lb live rock in tank
    Clowns, chromis, gobies, blenny, chalk bass, choc chip starfish and sand sifting

    Would anyone recommend skimmer?
    Water tests fine, occasionally 8.0 ph.

    • Jeff Kurtz says

      Thanks for your input, Brian! You’ll definitely endear yourself to Chris with those chalk bass. They’re right up his Caribbean-fixated alley!

      We’re definitely big proponents of protein skimmer use. Add one to your system, and I think you’ll be very pleased with the effect it has on your water quality.

      • Yea im really thinking about the instant ocean 100 skimmer…. Mostly for rapid evaporation causes my HOB to be noisy, and the cost of filter and carbon a month wud be eliminated.

        My concern is water flow, as I know the fluval 70 does well with that. Your thoughts? Wud the instant ocean 100 create as much water flow? Im limited on outlets so another powerhead in my 37 wouldn’t be too practical.

        Love the chalk bass. Awesome looking. Neat swimmer. Was actually in process of buying lantern bass before I realized I cudnt put that in with chalk bass. Getting my dream Christmas wrasse in this week instead.

        • Jeff Kurtz says

          Hmm, neither Chris nor I have any experience with the Instant Ocean Seaclone 100 (I think that’s the model you’re referring to), but I suspect it’s discharge wouldn’t create the same level of water flow in your system as your HOB filter does.

          Have you considered adding a sump to your system and then using a good in-sump skimmer? In that case, the return line from your sump should move a decent amount of water for you and wouldn’t take up much room in the display.

          • No room for a sump. I was actually persuaded by 2 LFS not to do skimmer for my 37 gal… Mostly because it’s FOWLR. And told more maintenance than Hob.

  2. Paul Baldassano says

    For mechanical filtration, I only use a diatom filter about twice a year. A diatom filter is a device that uses powder to trap very fine particles. After it is run for a few hours, it is backflushed and put away. I, unlike most people don’t feel detritus is a detriment to a marine tank (say that fast three times) Detritus is the end product of whatever we put into the tank and anything organic that is sloughed off the creatures in the tank such as coral and fish. Crustaceans, including copepod and amphipod shells and dead bacteria. Almost all of this can be used as food by the filter feeders in the tank and if there is any age to the system it should be filled with tiny tube worms which are filter feeders and live on this stuff. You don’t want to starve your feather dusters, do you?
    Pods, which are the staple food of many marine animals eat much of what detritus is composed of.
    A total lack of detritus is one reason new aquariums are not very healthy and are prone to all sorts of malady’s. The sea is full of detritus but you don’t see it accumulate to obscene levels as it eventually gets utilized by creatures on the low end of the food chain and the rest of it like shells, just disolve turning back into what it started out as. Sea water.
    If you use a mechanical filter, that detritus gets turned into nitrate by bacteria instead of being used for food by creatures that need it. I personally prefer linguini and clams and shy away from detritus, but who am I to judge?

  3. I only use filter floss in the first chamber of my sump witch I change every 2/3 weeks .

  4. Very confused……

    Just into the early stages of fish less cycling. I’ve got 2kg of Fijian lr in and about 18 kg of man made reef saver “live ” rock.

    I’m looking at a 200lph external with uv. Eventually also a skimmer and chaeto reactor. The tank is only 200 litres bug people tell me this is the way to go filtration wise.


  5. Very confused……

    Just into the early stages of fish less cycling. I’ve got 2kg of Fijian lr in and about 18 kg of man made reef saver “live ” rock.

    I’m looking at a 2000lph external with uv. Eventually also a skimmer and chaeto reactor. The tank is only 200 litres bug people tell me this is the way to go filtration wise.


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