In addition to the points already discussed, a number of other factors will determine what type of filtration you should use, and the specifics of its actual employment. For example, you should bear in mind that certain powerful filters, such as protein skimmers, and materials such as activated carbon will effectively remove fish medication from the water. It may, therefore, be necessary to isolate sick animals or to disconnect such filtration during the medication period.

Equally important is the effect of certain filtration methods upon trace elements. We have already mentioned that phosphates and nitrates, while harmful to some creatures in high concentrations, are required by certain algae for their survival. Likewise, a wide variety of minerals, trace elements, and other substances are utilized by many creatures in tiny amounts or, perhaps, only at certain times. Unfortunately, little is known about the specifics of the use of these materials or the exact amounts needed by aquatic animals. Therefore, it is prudent to routinely add commercially available trace elements, especially in marine aquariums, following the manufacturer's guidelines. You may need to do some calculation, and even some educated guessing, to fine-tune the amounts needed in your specific situation. The important point to bear in mind is that trace elements are constantly being removed from your aquarium by the metabolisms of the creatures that live therein, and that the use of certain types of filtration can accelerate this process.

The type of filter that will be most advantageous is also determined by the specific natural histories of the creatures that you keep. Animals that are notoriously slow to feed or that eat small amounts throughout the day, such as seahorses, will not fare well in an aquarium with a strong filter that quickly removes all the food items from the water column. Likewise, animals that are weak swimmers or those from placid waters will be stressed by strong currents.

Where strong currents can be tolerated, submersible powerheads can be used to create these currents in specific areas of your aquarium. Their location can also be changed regularly to ensure that uneaten food and other debris does not accumulate in undisturbed areas of the aquarium. Strong, alternating currents will stir up such material so that the filter can remove it.