Protein skimmer

The skimmer removes organic compounds from seawater before they decompose. It is considered the most important filter for a reef aquarium.

Detailed explanation

The skimmer works on a simple principle: it generates millions of micro air bubbles in a column of water. The organic molecules stick to the surface of the bubbles (they are hydrophobic, that is, they prefer air to water). The bubbles rise, dragging the organic molecules with them and form a dense foam that overflows into a collection glass. That dark, smelly liquid you find in the glass is stuff that would otherwise decompose into ammonia.

Sizing the skimmer correctly is essential. An undersized skimmer cannot keep up with the organic load. An oversized one costs more but does no damage. Better to abound.

For the type: long neck skimmers (cone skimmers) produce darker and more concentrated skimmate. Those with a classic cylindrical body foam sooner but with a more diluted liquid. For a serious reef a good cone skimmer is the best choice.

The skimmer goes in the sump, never in the main aquarium (with exceptions for nano reefs with hang-on skimmers).

In freshwater aquariums, the skimmer is not used because fresh water does not produce stable foam: the dissolved salts in sea water are needed to stabilise the bubbles.

Traditional skimmers are not used in koi ponds. Different systems are used: drum filters, mat filters, sedimentation chambers.

How it is measured

It is not a measurable parameter. However, the quality of the skimmer (colour, density, smell) indicates whether the skimmer is working well. Watery light green skimmate: glass is set too low. Dense brown skimmato: perfect. No skimmated: the glass is too high or the skimmer is undersized.

Related terms