If you plan setting up a reef tank, it is best that you forget about the need of any mechanical filters. Totally different to sweat water tanks, this might be more negative than positive, because they might act as “nitrate catapults”. Tanks running well, have crystal clear water without any mechanical filters. Avoid filter pads, Bio balls, Syporax or similar

within your tank, drain or technique tank.

But why is the water clean even if fishes are polluting it all the time? The answer is the so called

Nitrogene cycle

In well functioning tanks, invisible bacteria play an absolutely vital role! They control the “nitrogen cycle”.

  1. At the beginning of this cycle, and most critical in terms of toxicity, Amonium arises by excretions of fishes and fouling processes.
  2. Amonium is converted by bacteria into the clearly less toxic Nitrite. (Amonium concentration decreases, Nitrite-concentration increases)
  3. Nitrite is converted to the even less toxic Nitrate, again by bacteria. (Nitrite concentration decreases, Nitrate- concentration decreases )
  4. Nitrate is converted into nitrogen, again by bacteria, acting in anaerobe-milieu within substrate and sand. Nitrogen escapes the tank automatically.
  5. Nitrate (and also Amonium) is converted into algae growth

This process is going on all the time. In newly set up tanks it must first be established and stabilized carefully. This takes place in the so called startup phase which is needed for each reef tank before you add any sensible animals. In well running tanks, the amount of nutrients taken away by this process is = the amount of added nutrients.

Read also the F.A.Q. point “live rock” !

Phosphate circle

Phosphates come into our tanks by feeding, water brought new to the tank or objects within the tank containing phosphates. It can be deposited/settled.This is taking place in substrate and sand, water and adsorber material added to the tank. Phosphates also are assimilated by algae and can be removed together with algae.


Different to mechanical filters that just collect particles/excretions within the tanks circuit, skimmers remove them steadily.Also water is enriched with oxygen which is an important function especially in overpopulated tanksEven if some tanks also run well without skimmer, it is recommended to use a skimmer for your reef tank.

There are several more methods to run a reef tank (Algae refuges, Deep-sand-beds,..) or methods improving the natural filter function of bacteria like Zeolite filter, Vodka method ….