Protein skimmers are perhaps the most useful part of a modern saltwater aquarium. Oxygenated water, eliminates dissolved organic substances and wastewater helps us
A closed system mimics pristine reef waters. Most protein skimmers are not installed properly and offer only a minority of benefits. So, if you are looking to buy a skimmer or are considering whether your skimmer works well, here's a summary. You can also read more here about protein skimmers.
The main idea behind protein skimmers is to hang the best bubbles in the water as long as possible. This gives time for the loose residue to cover the balloon, rise to the top, and be removed.
For example, I'm going to use an old air-powered reverse flow model. The air stone at the bottom of the skimmer creates an upward flow. There is a water inlet from the tank near the top of the skimmer, and a water outlet at the bottom.
The trick is to let the bubbles hang but not push them out from underneath by adjusting the amount of water flowing downwards. This allows for maximum bubble coverage and maximum bubble density in the skimmer.
When you are setting up your skimmer you will want to set it up for your tank. In general, adjusting the air/water level in the skimmer tends to increase or decrease. If you remove the skimmer and you have brown debris in the tube but not in the cup, you will need to raise the air/water level.
This is done either by opening the valve to get more water out of the pump or if your pump is at its maximum prime you need to limit the amount of water that comes out of the skimmer.
If there is very clear, watery-looking foam in the cup, you can reduce the water/air level so that the foam lasts longer and then overflows.