From FrugalReef

Filtration is the black art of marine aquariums. It's really more like alchemy than chemistry. Just remind yourself that if there is a lot of controversy around weather or not a particular approach is better than another, both are probably pretty much equal.

In general, if you are using a thick sand bed, lots of live rock, and not overstocking a tank that has hide time to cycle sufficiently you aren't going to need much in the way of filtration.

The most common filtration systems I've seen being used by successful hobbyists in America rely primarily on the bacterial action in live sand and live rock. In addition there is almost always a sump with a mechanical filter, and water trickling over bio-balls. Large systems very often incorporate protein skimming. Many people like to grow macroalgae like Chaetmorphia in their sumps to control nitrates, while carbon filtration is usually pretty controversial.

Personally, I usually do not use protein skimming, but usually do like to use a Deep Sand Layer and a large sump with refugium to provide extra bacterial action and reduce the "load" by increasing the amount of water in the system.

The best way to learn more about filtration is to peruse some of the Aquarium Journals to see what other people are doing and use this as a reference. But first, read a few articles so you understand the principles at work.

• Nitrogen Cycle - The basic "why it works"
• New Tank Syndrome - What to avoid
• Cycling - How to avoid it

[edit] See Also

• http://www.advancedaquarist.com/2005/6/aafeature - Experiments testing Monaco (Plenum) vs Deep sand bed aproach