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Filtration For The Small Saltwater Aquarium

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The purpose of this article is to provide the new marine aquarist with an example of a simple, but effective, water filtration regime. It is specifically targeted towards small saltwater aquariums that do not utilise a protein skimmer.

This is, of course, not the only technique of filtration available for a small saltwater (SW) tank and does not intend to contradict other, equally effective, methods. This article also does not advocate the non use of a quality protein skimmer whenever it is possible. Using a quality skimmer will provide better water quality than this regime is capable of, providing other aspects such as proper feeding and stock selection are followed.

Setting up a new tank can seem confusing at times, especially when every fishkeeper you ask has his/her own opinion on "the best" way to do things. While this can be frustrating, in my mind, it is also what makes this hobby so interesting. So many dedicated people, so many ideas. The important point to consider, when studying one part of a plan, is how the system functions as a whole. This is why I have included all aspects of my water maintenance regime in order to address the use of a simple power filter. By this example I only want to answer the often asked question: "Can I, and how do I, use an ordinary power filter in my small saltwater tank?"

The effectiveness of this filtration system revolves around these main aspects:

  •  Understanding the difference of, and requirement for, both nutrient export and nutrient conversion;
  •  Use of live rock as natural biological filtration;
  •  Use of a simple power filter (with biological media removed) for mechanical filtration;
  •  Use of R/O (reverse osmosis) water;
  •  Regular, partial W/C's (water changes) combined with substrate syphoning;
  •  Targeted livestock feeding;
  •  Proper flora and fauna selection.
  • Part I: Understanding nutrient export and nutrient conversion

    Nutrients are introduced into the aquarium through the feeding of flora and fauna, their resultant waste products, and their natural growth, death and decay. Whatever the source, nutrients follow a general path of decomposition from solids to solution; from ammonia to nitrites to nitrates. This decomposition is accomplished first, by decomposing animals (Hermit crabs, brittlestars etc...) and further by decomposing bacteria (Nitrosomas and Nitrobacter).

    The great oceans of the world, and their currents, act to constantly dilute and remove harmful levels of ammonia, nitrites and nitrates from the reefs and coastal waters where most aquarium inhabitants are found. As a result, saltwater flora and fauna have not adapted adequate coping mechanisms and cannot tolerate elevated levels of ammonia or nitrites, and to a slightly higher degree, levels of nitrates. In our small, artificial environments, any filtration system must address this nutrient build up by either export or conversion.

    Nutrient export: This means permanently removing the nutrients from the water column (water in the tank). This can be done best with a protein skimmer, and to a lesser degree, with a power filter. The drawback to a powerfilter is that it cannot remove the very fine dissolved organic matter that a protein skimmer can and the nutrients are not actually exported unless the filter is cleaned. Another method of export, to remove fine dissolved nutrients and settled waste, is partial water changes, combined with substrate syphoning.

    Nutrient conversion: This is the changing of nutrients from solids to solution and from ammonia, to nitrites, to nitrates. As described above, this is performed by both decomposing animals and beneficial, denitrifying bacterias. Conversion takes the very harmful nutrients, such as ammonia and nitrites, and changes them into a less harmful form, nitrates. Another form of conversion involves the growing of various macroalgae. These primitive plants convert free floating nitrates into plant matter (leaves). This conversion can also become export if the macroalgae is then trimmed and harvested from the tank.

    To put this all together: We need nutrient conversion within our tanks to breakdown the very harmful ammonia and nitrites that will result from feeding, defecation and decay. However, even with very efficient conversion, there will come a point at which the less harmful nitrates will also reach "very harmful" levels. To counter this we need to export nutrients. The faster and more efficiently we do this - the cleaner and healthier our saltwater tanks will be.

    What is Live Rock?

    The two general conversion groups discussed above (animals and bacteria) inhabit the substrate and what is commonly referred to as "live rock" (it is the organisms in the rock that are alive, not the rock itself). Most live rock is very porous dead coral, harvested from the ocean. When determining the amount of live rock (LR) to use for natural filtration in your tank, a common rule of thumb is to add one pound of live rock for every gallon of water (about 100 g/L). This of course, is a general guideline and the correct ratio will depend on how lightly, or heavily, the tank is stocked with flora and fauna.

    So, the question is raised, "If we desire beneficial bacteria in the live rock - why do we avoid it in the power filter?"

    Good question...

    There are three main reasons why live rock use for biological filtration is better than other, artificial means.

    First; There is a wide assortment of decomposers found in live rock. In fact, one really doesn't know what one is getting till the rock has aged in the tank for a while. With artificial media (bioballs, biowheels, ceramics etc...) there are several beneficial bacteria strains and little to no larger decomposers. The larger spectrum available with LR means that nutrients are more completely and efficiently broken down.

    Second; The porosity, or "available surface area" in LR is such that large populations of bacteria can inhabit a relatively small piece of rock. If the same surface area were to be achieved by the use of bioballs, for example, a very large sump to hold them would be required.

    Third; Waste tends to be trapped and accumulate to a greater degree in artificial media. By doing so, it adds to the total nutrient load on the system. To understand this one simply has to open a filter that has been filtering a freshwater tank for awhile. Look at all that crud! It is all still effectively in the water column, building up large populations of bacteria that are converting and adding large amounts of nitrates to the water (hence the term "nitrate factories"). Live rock does build up waste as well, but to a lesser extent, and many of the lifeforms within it push the waste out of the rock where it can be syphoned away.

    Part II: Using a power filter for mechanical filtration

    When using a power filter it is important to remember that the saltwater application is different than the freshwater application. Here, we are only using the filter to trap and remove nutrient particles from the water (mechanical filtration). We are not building ongoing populations of beneficial bacterias (biological filtration). With this system it is also possible to use products like carbon or phosphate removers (chemical filtration) by placing these in the bio media chamber.

    In this example, taken from my own small tank, I am using an Aquaclear AC200 power filter, but other brands and styles of power filter can be used as well, with slight modifications for their method of operation. The main point is to remove the biological filtration element.

    Each week I remove the filter from the tank and clean it in the sink (unlike the freshwater practice of using syphoned tank water to clean the sponge to preserve cultures of beneficial bacteria).

    Here is a shot of the floss with a little more than usual detritus on.

    The fine filter floss (with all the gunk on) is removed, squeezed out and placed in the garbage. The sponge and filter box are cleaned very well under the tap. After cleaning I use a small container with R/O water (from the cooler) to soak the sponge in. Squeeze and repeat a couple of times to rinse out any leftover tap water.

    Next I apply a new layer of fine filter floss. This is polyester batting that can be purchased from the LFS or from a quilting supply store. A little goes a long way. The important thing is to completely cover the bottom surface of the sponge. Experiment with the uncompressed thickness. The final result should be 1 cm or so compressed.

    Here is the floss/sponge in the basket.

    And a shot of the filter back in the tank with the intake surface skimmer attached. This surface skimmer simply splits the filter intake so that some feed water comes from the surface and some from the mid tank level. It is made by Aquaclear and comes with various intake tube adaptors.

    *Warning* The fine filter floss must be changed regularly. Failure to do so will eventually lead to the floss clogging completely and acting like a water dam. The feed water will then push the basket, sponge and floss out of the filter box and may result in the filter overflowing.

    This method of filter use and maintenance is simple and effective, when performed regularly and combined with the following procedures:

    Part III: Partial water changes

    Using a power filter will aid in removing solid particles that are free floating in the water column but will not remove waste that has settled on the substrate and rock. There are also those nitrates (that are the end result of the denitrifying process) to contend with. These forms of nutrient/waste also have to be removed from the water column. This is acheived by performing regular partial water changes.

    The left photo shows the materials I use to manage this part of the regime.

    I use two buckets, one for my new mix and one for the tank water I will syphon. I have salt, R/O water (bottled) and a hydrometer for measuring the specific gravity (salinity). There is also a small powerhead to create current in the mix bucket (to keep things stirred up) and a thermometer and heater to match the mix temperature with the tank temperature (missing from the photo is my water test kit).

    I make up a new saltwater mix a day or two ahead of the regularily scheduled water change. I add the R/O water and salt till I acheive the correct salinity and then put it to one side with heater and powerhead running. Occasionally I move the powerhead around to make sure all the salt is dissolved. I also check with the thermometer and hydrometer to ensure the water is within the correct limits (the same as my tank).

    To keep the water changes simple, I replace 5 gallons (20 L) of water (1/6th the volume) weekly. To do this I use a simple syphon to remove waste and water from the substrate and rocks and then refill the tank with my new batch of water.

    How much water to change is a variable that depends on:

  • The size of the tank;
  • The bioload (flora and fauna) in the tank;
  • The level of feeding involved.
  • There is no set volume of water that should be changed. The aquarist simply experiments with the volumes until, by testing on a regular basis, the ammonia and nitrite levels are 0 and the nitrates are 0 or negligible in the tank. This is determined by using a good quality, saltwater test kit.

    Occasionally, waste will accumulate under and around rocks, polyps and corals. Even the interior of live rocks can use a good dusting now and then. To move this "hard to get at" waste out of the nooks and crannys, I use a very technical tool known as a pneumatic water transference device, a.k.a. "turkey baster."

    The way to use the baster is not to try to suck waste up with it but rather, to blow jets of water at the rock/polyps/corals. I do this in order to move waste either into the water column to be filtered or into the open to be syphoned. The first time you blow out a rock you will be amazed by the amount of gunk that has accumulated inside. Most of this is bacterial "flock" or waste. By doing this on a regular basis you can remove a fair amount of accumulated waste and avoid outbreaks of cyanobacteria (slime algae).

    The following is the schedule I use for my water maintenance:

  • Friday or Saturday: make up new saltwater mix. Put it aside and let it age.
  • Saturday evening: Blow out rocks and corals with turkey baister and clean front glass. This allows the new waste to be processed by the filter.
  • Sunday: Remove, clean and replace filter. Syphon water and replace with new mix.
  • Part IV: Proper flora and fauna selection

    Even if one adheres strictly to a proper water filtration program, ongoing issues of water quality can arise if the topic of livestock selection has not been properly considered.

    The simplest situation to contend with is that of fish only, without corals, polyps etc... In this case, waste can be kept to a minimum by low stocking ratios and targeted feedings. Targeted feeding simply means that food is directed at the fish with a feeding prong, tweezers, eye dropper etc...and only the amount the fish will eat is offered (no leftovers). This should also be done with anenomes and other corals, polyps etc...

    When selecting fish for the small aquarium, some care should also be taken to consider the mature size of the fish and its feeding habits. Those cute little yellow tangs and angels will grow to be far larger than your tank's capacity, and adding too many fish will overwelm even the best filtration system.

    Some fish are grazers and/or slow eaters, such as seahorses and pipefish. species such as these need to be fed more frequently and have food available for longer periods. This also increases the nutrient load on the tank.

    The situation becomes more complex when corals, polyps and filter feeders are introduced. Some corals, polyps anenomes etc... can be target-fed fairly specifically but others, such as filter feeders, must have their food introduced to the whole tank. This means intentionally creating a nutrient rich water column that must eventually be filtered somehow.

    As a small, skimmerless tank keeper I know this dillemna well. I have filter feeders such as non photosynthetic gorgonians, Hawaiian feather dusters, a coco worm and a chilli coral as well as the usual assortment of zooanthids, soft polyps and mushrooms. My choice is to either feed them a nutrient rich solution via the water column or to restrict their feeding, perhaps leading to starving and eventually to losing them. This choice of livestock, and its addition of excess nutrients means that I am constantly battling algae in my tank and am limited to the amount of fish my tank will "carry" or cope with.

    While this is just one example of the considerations revolving around livestock selection, it does serve to illustrate how the mix of flora and fauna in a tank can lead to complications in water maintenance. I will stop here, as compiling stocking lists and their effects would result in the need for a whole other article. However, I will say; the beginner SW aquarist should strive to keep these complications to a minimum, so that their first experience will be a positive one. In the end, each person must evaluate their commitment and skill levels and plan a tank accordingly.

    Well, that's it!

    I hope this article will help answer some of the questions that a new saltwater aquarist might have in regards to maintaining a small, skimmerless tank. If it does not answer most of the questions then at least, it should aid in pointing out the areas that one should further investigate. From this starting point, it is hoped that you will do the research, ask questions, develop a plan, and really enjoy your first successful saltwater tank.

    Good luck!        

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