An Observation on Protein Skimmers

The trendy reef technique today, seems to use the combination of the live rock in your display tank and macro algae in a refugium, plus a protein skimmer if the fish load warrants, or very high water quality is desired to keep delicate corals, usually the stony varieties. Heavy feeding of both fish and coral is also common practice. Some have achieved beautiful, heavily stocked with fish tanks, and delicate corals together in harmony, by heavy feeding i.e. 2-4 times a day, and the above simple filtration method. Obviously with lots of food entering the system, nutrient export is vital, thus the importance of fast growing macro algae tanks, and very efficient skimming.

The origin of protein skimming or the floatation reactor, like many of our filtration techniques came from the POO trade, more correctly sewage treatment.

It can be explained using the example of putting a drop of oil in some water. The oil spreads out into a single layer of molecules across the surface of the water. As the water is foamed the oil (organic substance) remains on the air/water border (bubble). As part of the organic substance is water soluble (acids) therefore sinking into the water, whilst most of the molecule is water repellent staying on the outside of the bubble. As the bubbles reach the surface, they burst and push foam up into the collection cup.

I couldn’t begin to count the number of manufacturers across the world of protein skimmers or foam fractionators, but they can be categorized in 4 groups concerning the method in which they create bubbles.

First and probably most simple and still sold today is the method of using air stones in the bottom of the reaction chamber, these wooden (to get a very fine bubble need to be replaced monthly.

Second is the venturi nozzle, requiring an impellor pump to push water through a nozzle that sucks air from a port in the nozzle. The water can either be drawn from the skimmer itself, making it a recirculating skimmer or directly from the aquarium or sump. The later method using only one pump but suffering from poor water to air mixture in the chamber and a lack of control over the amount of water passing through the chamber, leading to a short reaction or contact time. Large commercial models from around 400 litre reaction chambers and upwards commonly use this injection method in the recirculation mode using a separate pump to pump water into the chamber, while the venture or turbo pump draws its water from the bottoms of the reaction chamber where there are no bubbles and the skimmer outlet pipe originates. It has been said that venturi nozzles produce better foam in the instance of very high dissolved organic loads like those found in shark tanks.

Third is the Beckett injector. It’s basically a redesigned venture generally capable of generating finer bubbles. They commonly come as the 1408 and 2408 injector. These don’t normally come in recirculating models (although possible) thus limiting contact time despite the finer bubbles.

Fourth and most common in the arsenal or the “gun” reefer, the needle wheel. The impellor of a pump is replaced with a disc with needle like plastic knobs protruding from it. Some even use stuff that looks like steel wool. The air is injected directly into the impellor housing where it is broken into the water by the new impellor. This method continues to be developed with some single injector pumps like ATB’s XL cone skimmer using a Laguna 2400 motor and customized impellor housing drawing up to 3000 litres of air per hour whilst using 60w of power. The equivalent Deltec AP1004 using 4 Ehiem 1260 needle wheels uses 208 watts. Royal Exclusiv also boast similar efficiency with their Red Dragon pumps (also using Laguna motors) fitted to their renowned Bubble King skimmers. Korallen and ATB are both marketing their cone shapes as the way to go. It seems to make a smooth transition for bubbles toward the skimmers throat, with the neck of the skimmer a virtual continuation of the reaction chamber. Interestingly the reaction chambers of these larger capacity needle wheel skimmers seem to tend toward short and fat rather than tall and skinny. This maybe to fit under tanks but at around a metre tall the tank would be a long way off the ground! Maybe someone in the know can write a reply to explain this phenomenon. Is it something to do with the way the bubbles collide?

I’m often frustrated with the lack of factual information about a skimmers performance provided by manufacturers. They seem more intent on talking about how it looks, or some other throw away line like how much water can be pumped through it ( of coarse you can pump 920 litres per minute through a 100mm pipe!) rather than the correct through flow to maximize efficiency. But this is the commercial world……we’re just stuck in it as hobbyists.