Unfortunately, many new marine aquarists find themselves frustrated and unsuccessful because of inappropriate filtration techniques.

Wet dry filters (also known as trickle filters) are contained in a sump and consist of large surface- area media (usually bio-balls), over which tank water flows. The media is mostly suspended above the water level in the sump so that incoming water trickles through it forming a film. The high surface area provides both growth area for beneficial bacteria and for tremendous gas exchange. Because of their high capacity, wet/dry filters remain useful for very heavily stocked systems and large commercial systems. The reduction of nitrate to nitrogen gas requires anoxic conditions. The highly aerated conditions and they types of substrates in wet/dry filters prevent areas of anoxia from occurring, so nitrates accumulate. Specialized denitrifying filters exist, but these add a great deal of cost and complexity. While wet/drys do have their place, we will soon see that live rock provides more complete filtration with plenty of capacity for the typical home marine aquarium.

Live rock has become the foundation for marine aquarium filtration because it serves a variety of purposes very well. It provides a natural-looking and attractive substrate for aquascaping, habitat for ornamental animals, habitat for scavengers (amphipods, worms, tiny Sea Stars, etc.) and substrate for encrusting organisms that are both attractive and functional. While there is no direct harm in the use gaudily-colored artificial corals, ceramic ship wrecks and bubbling toy scuba divers (except perhaps for their insult to good taste. But hey - to each his own!), they will never match live rock for it’s diversity of habitat and the resulting diversity of life that it brings.

It is estimated that a typical morsel of food will be eaten 15 times before it has been reduced to pure waste. All of the amphipods, copepods, tiny Sea Stars and numerous other creatures that are introduced with live rock and make their homes in it’s labyrinth all need to eat! Missed food, fish waste and detritus are all processed naturally as they are eaten by these critters. With reasonable stocking and feeding levels, this makes mechanical filtration unnecessary or even undesirable in systems using live rock. This is especially true in reef tanks where mechanical filtration would remove the detritus and plankton that act as food items for corals.

The large surface area of live rock along with the varying oxygen levels in all of its nooks and crannies provides an outstanding substrate for biological filtration. Live rock on it’s own is quite capable of eliminating all inorganic nitrogenous wastes (Ammonia, Nitrite and yes, with reasonable stocking… even Nitrate).

In order to ensure that live rock stays "live" and functions well, some minimal maintenance must be carried out and basic care provided. An occasional blast with a turkey baster or powerhead will ensure that excessive detritus does not accumulate and clog the pores in the rock. Maintenance of proper pH, Alkalinity and Calcium (in that order of importance!) will ensure the good health of encrusting organisms, especially coralline algae. Healthy coralline algae will out compete nuisance varieties, so this is very important! Aside from these basics, live rock pretty much takes care of itself.

While live rock is expensive, it is not that unreasonable compared to the often inferior choice of a wet/dry or under gravel filter combined with artificial decorations. Live rock and the entire ecosystem that comes with it meets almost all of the needs of the typical filtration needs of the typical marine aquarium.

So what happened to that morsel of food that was mentioned earlier? Once it has been eaten for the fifteenth time, is it gone? Where did it go? Some of it did get incorporated into each of the critters that ate it, but each of those critters produced some waste. Ultimately, what remains is dissolved organic compounds (DOC’s). While DOC’s are probably not directly harmful, they can fuel the growth of undesirable bacteria and algae and they reduce light penetration through the water by coloring it. Fortunately, many of these DOC’s (usually proteins) have a part of their structure that is hydrophobic (is repelled by water) and part that is hydrophilic (attracted to water). This causes these compounds to be attracted to and form films at any air water interface. By creating a lot of air/water interface in the form of bubbles in a protein skimmer, these compounds can be concentrated as they form foam, and removed. Protein skimming has the added benefit of greatly enhancing gas exchange.

There is a mind-boggling array of protein skimmer designs and each manufacturer makes claims as to why theirs is the best. Here are some general guidelines: The flow rating (in gallons per hour) of the pump that runs the skimmer should be very roughly in the range of about five times the tank volume.

Live rock and a quality protein skimmer will usually cost more to establish than other filtration methods, but when thoughtfully considered the cost difference is often small. When the modestly higher cost is considered against fewer livestock losses, greater success in the hobby and greatly reduced frustration, it becomes clear that it is a bargain.

Available from companies on our saltwater fish dealers page.