The best type of filtration for your aquarium is the naturally occurring micro-organisms introduced in and on live rock. Live rock includes a range of critters, urchins, worms, crustaceans, molluscs, bacteria and algae, which all consume waste produced by your fish and assimilate it into their cells to be used as energy for their own biological functioning. The problem in many aquariums is that these micro-organisms that are so cherished by many reef fish are often depleted in any stocked aquarium. The only time you are likely to notice these organisms is when you look into your aquarium at night. This is best achieved with a torch as most of these organisms are nocturnal. Being nocturnal offers an amount of safety for them as they are able to move about while the fish are sleeping.

Creating a safe place for these micro-organisms to thrive will provide many benefits to any aquarium. One of the most modern styles of filtration now is a system known as a refugium, which basically means refuge or safe place. This is a separate aquarium often under the main tank which is connected by plumbing so they both share the same water. The refugium will contain room to allow your heaters, skimmers and pumps to be kept out of view from the main tank. The refugium should also have a pre-filter to stop the sediment from the main tank choking the refugium over time.

Macro algae, like caulerpa, are placed in the refugium to offer reverse photosynthesis and help filter the water. The lights on the refugium are best run when the lights on the tank are off, this helps to stabilize pH and gas exchange. It is important to add an iron supplement such as Red Sea Green if running macro algae in a reef tank. The iron will help stop the algae from crashing and reduce phosphate. The thriving algae will grow and soak up organics including nitrate and phosphate from the water. As the algae overgrow the refugium, you can harvest the algae out of the system, therefore removing these organics too. Remember that some caulerpa is noxious, so it is best to destroy the algae you remove. Some macro algae will be eaten by your fish and can provide a great free feed.

The medium of the plenum is sand which will create a place for these organisms to live. 4 inch of 1mm coral sand is perfect. A plenum is a small void of water which is often put under the sand to allow horizontal distribution of oxygen. The plenum is created by placing some 1inch thick mesh or pipe then egg grate covered in fly screen on the floor of the refugium covered in sand. There is much debate over the correct depth of sand but I have found that it all works since the majority of the work is done by assimilating algae on the top layer. Micro-biologists have found the refugium will work most effectively if offered light to stimulate the assimilating algae. If there is no light and the algae is not present, the bacteria will play a more significant role in this process which is otherwise dominated by the algae if light is present.

I often hear people comment on how much waste their fish make. It is important to understand that all of the nutrients that enter your aquarium come primarily from the food that you feed your fish. Fish that increase the need for food to be added to the tank will decrease the quality of the water. Fish that scavenge and donít require additional food other than what is already there are capable of providing beneficial effects to the system. Ensure you only use high quality fish food and never overdo liquid invertebrate foods. A balanced aquarium achieves biological allocation which means for each bit of organic waste being produced there are biological processes present that are able to use the waste for assimilation, allowing the aquarium to function as a stable ecosystem.

A protein skimmer is not essential for an aquarium with balanced biological allocation. It is easy to do a three week test to check the functioning of the skimmer. If you donít add any trace elements or supplements for three weeks and the skimmer keeps on skimming, then the skimmer is valuable to the system. If the skimmer only starts to work again once you replace the trace elements then the aquarium in its current state has biological allocation and the skimmer is not an important piece of equipment to that system. Systems with pure nitrifying filters such as bio-balls will always benefit from the addition of a skimmer as they will never achieve biological allocation.

The food goes into your aquarium and eaten by the fish and invertebrates. The chemical waste from the fish is assimilated by algae and the solid waste is eaten by scavenging fish and micro-organisms. The waste from the micro-organisms and fish is broken down by nitrifying bacteria. The waste from the nitrifying bacteria is broken down into nitrogen gas by the denitrifying bacteria. The result of the food once all the energy is used by the biological processes within your aquarium is a non-organic detritus called mulm, which looks like concrete dust. It is important that the mulm is removed from the system using mechanical filtration or vacuum siphons. If the mulm is allowed to build up, it may result in the formation of poisonous hydrogen-sulphide produced within a deep layer of mulm also know as a dead spot. The accumulation of mulm is one of the main reasons for so called ëold tank syndromeí.

The micro-organisms thrive in the refugium and many of them find their way back into the aquarium helping to recolonise the main tank and provide a great food source for its inhabitants. The use of a refugium will dramatically increase the cultures of organisms in your live rock and sand, making it far more effective as a filter as well. Without the use of a refugium, the entire population of beneficial micro-organisms like amphipods and copepods can be wiped out by specialist feeding fish.

To allow aeration, the top layer of the refugium should be stirred regularly. When the refugium is stirred you will often see the corals open up and feeding on the plankton which is pumped back into the main tank. No matter how tempting it is, it is recommended not to keep any fish in the refugium or it is not a refugium. With time the varieties of micro-organisms will become limited, reducing the efficiency of the system, so it is a good idea to add a small piece of fresh live rock to your refugium a couple of times a year to ensure that a fresh culture of micro organism is introduced to your system.

The larger the refugium, the better. It will be able to support larger cultures of beneficial organisms, working much like a compost heap. A larger refugium also adds to the overall water volume of the tank, allowing better waste dispersion. Many smaller hang-on refugiums are available that are easy to install and can benefit any aquarium.

It is worth getting a flash light and a magnifying glass out and looking in your tank at night once your lights have been off for a few hours, so you can see the mass of nocturnal micro-organisms that are each playing their role in keeping you aquarium beautiful. Every healthy aquarium will have a huge culture of micro-biotic life. The idea with the refugium is to encourage and increase this process because of its cheap running costs and amazing results.

If you use a UV it is important not to run it all the time as it will decrease valued micro-biotic life. I would run it for one month after a new fish is introduced or anytime you suspect a fish maybe suffering from a disease.

Keeping a magnificent aquarium that just survives is no longer the mystery that it once was. You must aim for your aquarium to thrive not just survive, if it doesn't thrive its time you get up to date with modern knowledge and technology. Itís all possible now.

Good luck and enjoy Paul Talbot