Hey fellow Saltwater Aquarium fans,

Basically as I’m sure you have realised you almost need a dictionary and a marine biology text book to cope with all the terms and jargon in this hobby! I actually find this pretty cool as I love to confuse my wife and friends ;)

Today I’m going to introduce to you a couple of unique aquarium filtration options you may or may not of heard of and explain what they are and what they do.

1. The Plenum: Sounds weird but can actually be amazingly helpful for an aquarium. A Plenum system is a type of biological filter that uses a deep bed of live sand (micro and macro organism packed sand from the sea) suspended an inch or so off the aquarium bottom as the biological filter that contains both aerobic (removes ammonia and nitrite) and anaerobic (removes nitrates) areas in its depth which is traditionally about 5 inches.

The Plenum system (also known as a Deep Sand Bed or “DSB” filter) was developed by a very smart Dr Jaubert (and so is also known as the Jaubert system, argh so many names for this one thing!!!!) for keeping his reef aquarium heathy. The plenum itself is the oxygen free lower level of sand/gravel suspended by a plastic grid on supports above the aquarium base so that warm water (generated from the anaerobic conversion of nitrates into nitrogen gas) can drift up through the filter and removes any harmful hydrogen sulphide build up in the sand bed.

Bluestreak Cleaner WrasseThe surface of the plenum system will be packed with sand stirring filter feeders aerating and cleaning the top layers of live sand that contain the aerobic bacteria, sand sifting Gobies and Wrasses add to this effect.

When a Plenum filter is used in conjunction with a protein skimmer it is a very effective bio filter especially because of its nitrate reduction. It works best when the reef is suspended above the plenum using glue or epoxy resin for maximum water flow and so filtration. A possible downside is a buildup of harmful hydrogen sulphide if there isn’t sufficient water movement upwards or sand sifting at the top.

2. The Refugium: A place to harbour refugees under your aquarium! No really it is; a ‘fuge is a tank  separate from the main aquarium with (usually) shared filtration and its own lighting either beside (hang on style) or beneath the display tank (like a sump) to put delicate, sensitive species so they can be free of predation at the hands (or fins) of fish, that would occur if they were in the display tank. In fact the refugium has many possible uses:

  1. A quarantine tank for new arrivals.
  2. A treatment tank for medications (treatment has to be safe for the main tank or have separate filtration though).
  3. A quiet place for the bullied or bullies (naughty corner!) to go.
  4. A system to raise shrimp (algae, amphipods, copepods) to feed the display tank or just as additional pets.
  5. A place to keep live sand, grow some plants to help with water quality.
  6. A place to add gear without messing with the display tank.

As well as having all these possible uses the refugium increases the total water volume which is good for making the water stable, increasing buffering capacity and dilution of nasties in the water, obviously the bigger volume of your refugium the better.

3. Berlin system: If you are thinking this has got something to do with German saltwater tanks you are right! Some clever Germans in Berlin came up with a new take on filtration also known as the “natural system” that is based around the use of large amounts of live rock as your biological filter. The Berlin system remains the filtration system of choice for reef aquarium purists as it is very natural, after all Live Rock is the biological filter of the worlds coral reefs.

Live RockThe Berlin system uses Live Rock as the aquarium’s biological filter as it is packed with beneficial bacteria that will convert ammonia into nitrite, then nitrite into nitrate and even has oxygen free zones (anaerobic) within it containing  bacteria which convert nitrate into harmless nitrogen gas. This is the Berlin systems natural nitrate reduction (NNR) system.

Along with the Live Rock (housed in the aquarium itself or in the sump) there is a big ol protein skimmer which aids filtration by removing much of the marine life’s waste and uneaten food at the source before its converted into ammonia making the bacteria’s job easier. There is also no substrate, to help the protein skimmer suck out all the detritus unhindered.  And thats about it, very simple, natural and highly effective. I have run a system like this before and it ran like a dream!

The advantages of a system like this is the fact that it looks appealing and is letting nature do its job, its also relatively simple, cheap to set up and looks really good (I absolutely love Live Rock!). The only real downside is the bioload a system like this can sustain; you can only put so much livestock in for the amount of Live rock you have because there is only limited surface area for the bacteria to grow to deal with this waste.

I hope this article helped to shed some light on some different biological filtration options available to the saltwater hobbyist.

Your marine aquarium maestro.

Saltwater Aquarium Advice