To describe the principle or function of a protein skimmer one could simply say that the filter material of a common filter system is replaced by air bubbles. Sander's protein skimmers are designed as counter current protein skimmers. The water enters the protein skimmer at the top and flows down to the bottom. The air is introduced near the bottom by wooden air stones or sucked in by an injector (venturi) and small bubbles rise against the water stream to the top. The airflow should be sufficient enough to fill the cross area of the protein skimmer.
When designing our protein skimmers, great attention was paid to obtain a relatively large volume to get nearly laminar flow conditions. This is very important for the contacting of the air bubbles to the protein compound as well as to the waste particles. High turbulences in a protein skimmer may look nice but they result in a break off of the contact between the air bubbles, protein compounds and waste particles and will consequently reduce the foam efficiency remarkably. When the air bubbles have passed the reaction tube of the protein skimmer they reach the water level and together with waste particles and proteins they form a viscous foam in which proteins link the air bubbles and the waste particles.
The following reaction can be described:
- Undissolved surface active solids can be deposited on the interface between water and air and thus be concentrated in the foam.
- Undissolved, non surface active solids can contact dissolved surface active compounds, and then be concentrated in the foam.
- Dissolved waste material can partially be oxidized by ozone, so that the rising air bubbles can contact them.
The waste foam built up in this way will be transported by the upwards streaming airflow via the foam tube into a foam beaker. On the way through the foam tube the foam is drained so that excessive water flows back into the protein skimmer, and the water loss is minimized. The foam itself becomes concentrated. At the end of the foam tube the foam should "grow" slowly and relatively dry out of the foam tube and fall down into the foambeaker.
The common protein skimmers have a foam cup that can be removed easily and cleaned under the tap. Furthermore at some skimmers it is possible to connect a tube for draining off the waste foam. The "Helgoland"-Skimmer has a special water rinsing ring nozzle which washes off the foam continually.
- The protein skimmer removes protein compounds and other organic substances before they are decomposed to toxic substances.
- Waste and toxic substances which have been foamed into the foam beaker are totally seperated from the aquarium water and it's circuit!
- 3. Water which has passed the protein skimmer is purified of waste and furthermore highly enriched with oxygen which is essential for aquatic life!
Protein skimmers can only be used in salt water aquaria. The diagram below shows that already at a salt concentration of only 10 per mille bubble diameters of less than 1 mm are found. This is of importance as the smaller the air bubbles the better the contacting of the bubbles to waste particles. So protein skimmers do not only work in water with a high salt concentration, as the Red Sea or Pacific water with 35 per mille and more, but also in water of the eastern seas with only 15 per mille. Indeed, a protein skimmer cannot be used in fresh water, as the air bubbles in fresh water with approximately 4 - 5 mm in diameter are too large for protein skimming. In salt water there are good results for quite different species of animals. So protein skimmers are used successfully for invertebrates and crustacea as well as for fish, for ornamental fish as well as fish for food, in the home aquarium as well as in public aquaria.