Counter-Current Skimmer

The counter-current skimmer also known as "air driven" has been around for a long time. They are probably the least expensive of all the different types you can buy or make.

They operate on a very simple principal. An airstone, made of wood, glass or ceramic is placed into the bottom of a chamber and hooked up to a standard air pump. The airstone needs to be very porous to create fine air bubbles. Most of the time a separate pump is needed to provide flow back to your tank or sump.

Water from your tank is injected into the chamber near the top. This forces the water against the rising bubbles and gives you a long contact time. Finally water exits from the chamber at the bottom and goes back to your tank or into your sump, depending how you have plumbed your system.

The best airstone with the finest bubbles are made of wood. This system, because of the separate air and water pumps, provides good contact time with the bubbles, so it removes a lot of protein per bubble.

The drawback is that it takes longer to remove that protein, because of the low flow rate. They also require more maintenance than other types. The airstone need to be cleaner and/or replaced relatively often. Another problem is the air pump. The quantity of air required means that you will need a powerful pump to push that much air.

Lastly, counter-current skimmers work best if they are tall. It’s not uncommon to see one 4 or 5 feet tall.