Protein Skimming
Protein skimmers are a must for a decently stocked saltwater tank as they strip dissolved organic particles from the water before they can be converted to nitrates.
There are simply too many models and manufacturers to discuss all of them, but the two basic designs are air-driven and venture:
Air-Driven Protein Skimmers
Air-driven protein skimmers use a wooden or glass air stone to produce bubbles in a column of water.
Venturi Skimmers
Venturi skimmers use a venturi valve to inject bubbles into the water column. Both air-driven and venturi have co-current and counter-current designs, with counter-current protein skimmers being far superior to co-current models.
In deciding on a protein skimmer, there are some basic things to consider. Air-driven skimmers use air stones which must be replaced on a regular basis (usually every month or so). Additionally, they usually require more maintenance than venturi skimmers to maintain proper skimming. Venturi skimmers on the other hand require very powerful pumps to achieve effective protein skimming. They are usually more expensive than air-driven skimmers as well. Also, any skimmer smaller than 24" should be avoided for heavily loaded tanks.
Cost of the Skimmer
Whichever type of skimmer you buy, the final cost of the skimmer must not overlook the need for an external water pump and potentially an air pump. A $200 venturi protein skimmer usually doesn't include a $150 high pressure pump; a fact that most people seem to miss the first time around.
