Behavior of two or more skimmers in an aquarium

Protein skimmers are interfacial adsorbers and operate by means of buoyancy. If they had ideal properties with an efficiency of 100 per cent, they could keep the cellulose and protein level in an aquarium at almost 0.0 mg/l. In reality, however, the values range around 0.4 mg/l, which is an excellent value in view of the varying surface tension of the tank water (during feeding, for example) which has an influence on the skimming performance.

After all, an ecosystem like a reef aquarium also needs a certain quantity of protein for its food web. Apart from the fact that aeration is out of place with skimming in an aquarium because it binds proteins, the question actually is whether it Is sensible to use two or more skimmers in a closed system (aquarium).

Many years of observation have revealed that only the use of skimmers of the same type, i.e. of same make, model and performance, is sensible. Even in this case differences in the skimming amount will occur as a consequence of slight manufacturing differences or settings of the air quantity. A large skimmer alongside a smaller skimmer will tie up the latter.

The following hypothesis can be made to explain this phenomenon: The foam discharge zones of skimmers behave towards the protein-containing surfaces of an aquarium comparable to the resistance towards the discharge of the water The ideal skimmer thus would have an extremely low resistance. A smaller skimmer alongside a larger skimmer thus cannot be a recommended choice because almost all protein will be removed by the large one. This is especially true considering that larger skimmers are less sensitive (speaking generally) to variations of the surface tension and thus operate more stably.

If, however “the stable door was locked after the horse has bolted” and two skimmers of different performances have already been fitted, then a distance between the two units as large as possible Is recommended. The removal of the protein particles by the skimmer with the larger performance has less effect then on the other skimmer. Of course a large distance between the units Is also sensible even in cases where the two skimmers are of the same type or have identical efficiencies.

Aquarium Ecology. Pages. 43-44. TUNZE Aquarientechnik GmbH, D-82374 Penzberg, Fed. Rep of Germany

The 6055 and 6095 Nanostreams are different machines altogether. Though they have the same general size, shape and footprint of the three smaller Nanostreams, their inner electronics are much different. The 6055 and 6095 operate on DC power. This makes them fully controllable, either by using one of our controllers or else with the use of another manufacturer’s controller. The controllable powerheads are much more sophisticated and so have a higher price tag, with the 6055 and 6095 retailing for $235 and $269 respectively.

Let’s first look at the flow rates and efficiencies between the 6055 and the 6095. The 6055 moves 1450 GPH and consumes 18 watts at full power. The 6095 moves 2500 GPH and consumes 21 watts at full power. At first glance it would appear that the 6095 is the clear winner here. It provides a nominal 72% increase in GPH flow while only requiring an additional 17% power consumption. This seems like a very good trade.

But flow rates in gallons per hour never tell the whole picture. The 6095 was designed specifically to produce a very wide flow pattern. By opening up the slots on the intake screen, the inflow of water is less restricted. This allows the propeller to pull in more water. Additionally the 6095 has a wider outflow nozzle, producing a much less directed flow pattern, but allowing the propeller to push out more water. The less restrictive nature of the 6095′s inflow and outflow designs allow it to move more water and to move it more efficiently.

But there’s no such thing as a free lunch and the 6095′s gains in efficiency do come at a price. That price is velocity. The wider flow pattern of the 6095 leaves the pump at a slower speed than the water leaving the 6055. Remember that the 6055 has a more focused outflow nozzle. This narrower nozzle serves to collimate the water as it leaves the pump, producing a narrower but higher velocity stream. This stream is capable of moving a greater distance. This increased range is the main advantage the 6055 has over the 6095.

To summarize, the 6095 Nanostream produces a flow stream that is approximately 2-3 feet around a reaches 3 feet. The 6055 Nanostream produces a faster moving stream that’s about 18 inches around and reaches over 4 feet. Though the 6095 is almost always the better choice for aquariums 3 feet or under in length, longer aquariums or those requiring higher velocity or more targeted flow can often make better use of the 6055 instead.

Die test of the 6055 Nanostream

Die test of the 6095 Nanostream

Fluid dynamics is normally something we can leave to the people with lab coats and multiple degrees. But then, reef aquarium enthusiasts aren’t know for shying away from technical matters. The reef aquarium hobby is probably one of the most cross-disciplinary hobbies there is. It involves elements of chemistry, biology and physics, and it involves all of these on a more than superficial level. Many long-time hobbyists point to this as one of the reasons the hobby has kept their attention and attraction for so long. While the chemistry and biology sides receive the most attention, the physics of moving water is also frequently discussed.

Yet one of the difficulties encountered when laypeople need to discuss technical matters is finding the right words to use. Formal science goes to great lengths to define terms with exacting specificity. The lengths forum members go to in defining terms can be notably shorter. Nevertheless with enough patience and questioning, even the most untechnical person can learn a lot about the science of saltwater aquariums and find ways to use this knowledge to directly improve the health of the aquarium inhabitants.

The term we’re looking at now is ‘undertow’. It’s a term that comes up fairly regularly and it’s almost always surrounded by a small cloud of vagueness. This vagueness of terminology is a problem. If we’re not exactly sure how we define it, or to what we attribute it, then we’re not really able to assess its value. To that end we can simplify the discussion by first agreeing that undertow in the ocean is something quite a bit different. While the ocean’s undertow is a function of tidal and wave action, things for which we do have corollaries in the aquarium, it’s also greatly affected by topography, which is far less relavant to the aquarium setting.

Undertow in an aquarium can then generally be defined as a laminar movement of water. It’s the movement of water at the lowest strata, just above the sandbed, moving towards whichever flow device is powering it. So how does a flow device create undertow in an aquarium? Remember that any pump that pushes water, also pulls water. As water is ejected from the front of the pump, an equal amount of water must be pulled in from the sides to replace it. (It’s easy to see why this must be true; if it wasn’t, then a pump would push away all the water around it and be left sitting in a hole of air in the aquarium.)

Now when a pump is pushing a relatively wide stream of water away, then there’s less room for the returning stream of water to return. And as with so many things in nature, the returning water follows the path of least resistance to get back to the pump. When a wide flow pump is placed towards the top of an aquarium, as they generally are, and the entire top section of the water column is moving away in one direction, then that path of least resistance is down low, right above the sandbed. It’s ‘easiest’ for the water to return in that lowest layer, so that’s what it does. That is what creates the undertow.

What we can learn from this is that undertow is not intrinsic to any particular pump design. It’s a function of many factors: the flow rate and stream shape of the powerhead; the powerhead’s location within the tank; the size and shape of the aquarium itself; and the arrangement of structures within the aquarium. It isn’t really something that the powerhead alone can take credit for, though powerheads with wide flow do make it easier to create an undertow that’s easy to notice. Viewed in this light, an undertow is more of a side effect than it is a goal.

By identifying the conditions that lead to a clear undertow we can begin to determine if the benefits are worth the costs. Is it more important to have an undertow, or would aquarists be better off focusing on the quality of the flow in the upper stratas of the aquarium where, after all, most of the flow-loving corals reside? This line of questioning gets us closer to our goal of correctly prioritizing the merits of different flow devices and our strategies for their placement and use inside the aquarium. It’s a topic that deserves more discussion and understanding.

The DOC Skimmer 9410 (top left) looks like what most people have come to expect protein skimmers to look like. It has a cup on the top, a pump on the side and a stand pipe next to that. It’s high quality clear acrylic with the fit and finish people expect to come out of Germany. Like most skimmers on the market it has everything exposed for you to see. The pump is right there, you can look in and see the bubble column… nothing is hidden from view.

But the 9011 keeps it all hidden. It is a simple, dark, unobtrusive box, following the classic form of our Comline series of filters. It has an internal pump and can be used in-sump with the included stand pipe sump kit (pictured below) or else in-tank without it (as it’s pictured above). For in-tank protein skimmers, it is the best on the market.

The 9410 is the more powerful of the two. It’s powered by a pump from our Hydrofoamer series (pictured below) which uses a needlewheel/Venturi combination to inject a dense column of tiny bubbles into the reactor. It’s by virtue of the needlewheel that the 9410 is able to produce bubbles which are, on average, smaller than those of the 9011. Smaller bubbles equates to a greater total bubble surface area which translates, loosely, to higher performance. This also makes it more electrically efficient, consuming 15 watts to the 9011′s 22.

The 9011 does not have a needlewheel. It relies on a permanent-magnet centrifugal pump (below) coupled with a carefully engineered Venturi to introduce air into a column of water. This allows the 9011 to process more water in the same amount of time, but not quite as thoroughly as the 9410. It does however give it a different advantage- a slight reduction on the decibel meter. The 9410 has never been described as loud, but if absolute silence is the target you are shooting for, you’ll hit closer to it with the 9011.

Another of the 9011′s advantages is that it can be used both inside the display aquarium or else down in the filter sump. This versatility can come in very handy if, for example, you plan to have a simple sumpless aquarium now, but foresee changing to a system with a sump in the future.

And one final distinction is that the 9011 has been designed to be more tolerant of changes in the water depth. It will operate quite happily at any depth between 4 and 11 inches. But the 9410 is like most protein skimmers in that it prefers to stay in water that’s a consistant depth. That can be anywhere between 5.5 and 9.5 inches, but it will require an adjustment if the level changes by much.

So there you have it, the main differences between the 9410 and the 9011 DOC Skimmers. While the 9410 does have a performance advantage, the 9011 has many of its own talents that deserve consideration.

The Interzoo Pet Product trade show takes place every two years in Nuremberg, Germany. It’s the world’s largest show of its kind and it’s also just down the road from the Tunze headquarters, where all of our products are designed, tested and manufactured. At the 2012 Interzoo we unveiled the newest member of our extensive skimmer line, the DOC Skimmer 9004. The 9004 is a complete redesign, from the ground up. It has an entirely new way of operating; everything from the pump to the collection cup is different. Compared to the 9002, the 9004 is more powerful. We rate it for aquariums up to about 65 gallons as opposed to the 9002′s 50.

So which skimmer should you choose? Choose the DOC Skimmer 9002 if you have limited space. If you intend to put it in the back of an all-in-one aquarium, the 9002 has a better chance of fitting. You should always double check the space you have to work with against the skimmer’s dimensions (and suggested water level). But it’s safe to say that the narrower footprint of the 9002 will mean it will continue to be the most popular choice for many. Many have asked us if the arrival of the 9004 means the 9002 will soon be retired. Since it remains so popular and since it fills a niche which no other skimmer can, we plan to continue making it for many years.

Now, on to the 9004. The 9004 is an excellent choice if you’re looking to make your own all-in-one sumpless aquarium. Here’s the 9004′s main advantage- it has a genuine surface-skimming intake. That’s right, it’s designed so that water sheets from the surface down into the skimmer. This is absolutely critical for a skimmer to perform. Most of the organics in a tank will collect on the surface, resulting in an ugly oxygen-blocking film. If that film is not skimmed away, the water quality suffers. There’s a diagram at the bottom that shows the general path water takes through the 9004.

The bottom line is that the choice between a 9002 and a 9004 comes down to space. If your space is limited, the 9002 has a better chance of fitting. Otherwise, go with the 9004. Either way, we’ve got some serious skimming in store for you.

For small aquariums, a stable osmotic balance is important, because they are particularly sensitive to constantly changing salt concentrations. The Osmolator® nano which was specifically designed for this, is a water level controller with only a single sensor and is equipped with a processor-based controller that protects against overdosing. It is suitable for nano aquariums or small aquariums up to 200 liters (55 USgal.). The sensor with magnetic holder is light-protected and can be positioned at any desired location on the glass panel.