Protein skimmers are designed to remove dissolved organic compounds (DOCs) from water before they decompose by means of a principle called Foam Fractionation. These compounds are hydrophobic or hydrophilic, or both- that is, they repel or are attracted to water, respectively. In a water molecule, the two Hydrogen atoms lend a slightly positive charge while the Oxygen atom slightly negative. The nonlinear arrangement of the water molecule gives it a slight electric dipole moment; we can also say water molecules are dipolar (non-polar molecules tend to be hydrophobic). The dipolar property of water is actually the basis for some of its most important and unique features, but I digress... the point is, many of the undesirable compounds in the tank, due to their hydrophobic character, readily "stick" to a surface between water and air.
Foam Fractionation involves the creation of many tiny bubbles to create a vast amount of surface area between water and air. These bubbles are created by various means (venturi pressure, spinning needle-wheel, airstone, etc) and confined within the body of the skimmer. Tank water passes through the base of the skimmer, and when a hydrophobic or partially hydrophobic molecule (as well as some types of particulate matter) meets this interface between the air and water (a bubble), it gets stuck, becoming bound to the bubble surface. The only way up and out for these bubbles is through the columnar opening of a collection cup which sits on top of the skimmer. As the bubbles collect an increasing amount of material, they become more frothy and disgusting... eventually reaching the top of the column and spilling over into the collection cup. This overflowing gunk is called the "skimmate"; that which was skimmed, I suppose. One may choose to "skim wet" or "skim dry", the difference being the amount of water removed with the skimmate. This is a direct result of the amount of bubble production and water surface height within the column. Skimming dry produces a nasty, stinky sludge in the collection cup but does not remove as much as skimming wet, which produces a steady amount of tea-colored liquid. The latter typically removes more DOCs but at the cost of also removing salt water, complicating top-offs because the water level fluctuation is no longer due to evaporation alone. Maintaining a strictly constant salinity is a little more difficult with aggressive skimming in a small tank like mine.
Two things determine the quality of a skimmer: (1) greater surface area between water and bubbles, and (2) contact time between the water and air. This is why larger, taller skimmers that produce a greater amount of smaller bubbles do the best.
Long story short, I had decided to buy and use a skimmer. Reading the countless reviews, testimonials, and personal experiences out there convinced me that the best one on the market for a Biocube29 is a Tunze Nano 9002 DOC Protein Skimmer. I asked my friend about his experience with them... as it turned out, he had one that was unused and was willing to lend it to me before I made my decision on whether to invest. This was great news... that very night I went home and disassembled, cleaned, studied, and reassembled it. It's actually quite a simple design but is very effective. It uses a venturi pump to produce bubbles; the aperture can be controlled using the small blue screw at the top of the chamber.
As most other Biocube owners have experienced, there is only really one option for placement of this skimmer: chamber 2. This entire chamber formerly served as my refugium, lit on a reverse-day cycle to grow chaetomorpha. I also used the drip tray to support a piece of filter floss which catches particulate in the overflow from chamber 1. Pictures of this are visible a couple of posts prior to this. Placing the Tunze in this chamber seemed problematic with a bunch of loose macroalgae tumbling around in the water. I didn't want the pump intake clogged with loose algae and the skimmer takes up more than half of the chamber, so I temporarily removed all of the algae until coming up with a suitable solution. My chaetomorpha happily lived in a separate bowl of tank water for a few days. The couple of unfortunate amphipods that migrated into the bowl with it were eventually fed to my fish who are still in the hospital tank.
The stock collection cup on the Tunze 9002 is, in my opinion, unnecessarily large for the profile of the skimmer itself. Its diameter exceeds the width of the back opening of my hood and the width of the back chamber. Some modifications to the tank and to the hood were needed so that I could easily remove the cup for periodic emptying. Out came the utility knife, heavy-duty scissors, and wire cutters. There are some alternatives and custom 3rd party accessories for the biocube which are meant to work in conjunction with the Tunze 9002, but I decided to just mod the tank for now. None of my proposed changes affected the outside aesthetic of the tank hood.
Slots cut out of the hood so that the cup can be removed with ease. They aren't apparent when the lid is closed.
The cord is extremely short. I had to add another power strip in the top shelf and cut a space make a shorter path from the skimmer to the plug.
I needed a way to get my chaetomorpha back inside chamber 2, protected and confined to a single area where it could be illuminated at night for growth but without risk of being sucked up into the skimmer. Even though the skimmer removes many of the nutrients that would otherwise decompose and be used by the chaetomorpha, it doesn't hurt to have additional means of removing phosphates and nitrates as they inevitably build up (the main method being regular water changes). The chaetomorpha is also handy for providing an environment where pods and other animals can thrive and reproduce. One of my concerns with a skimmer is that using it would suck up many of the pods that had been living and reproducing in chamber two, but judging by the frighteningly overwhelming population in the main tank I don't think they need much help reproducing. I thought about this at length and tried to come up with a home-made solution that would provide the same functionality as some of the pre-built 3rd party modifications.
For $3.99 I bought a clear, cylindrical plastic spray bottle at the supermarket that looked like it would fit next to the skimmer in chamber 2. Using the utility knife, I carefully started three rings of holes around the base of the bottle and progressively opened them until I could punch a small nail through each. I followed up with a much larger nail to open the holes to the desired final diameter, and tested the flow through these holes in my kitchen sink. Even with the water blasting into the opening of the bottle, the water level did not reach a couple inches higher than the top ring of holes- water flowed very quickly through the bottle. This is what I wanted. The mass of chaetomorpha could sit at the bottom of the bottle, lit up from behind the tank by my JBJ Nano Glo, with water flowing down from the top of the bottle to keep the spaghetti-like clump from dispersing and to provide necessary nutrients to the macroalgae. I opened up the top of the bottle so that water could easily pour in. Instead of cutting the top off completely, I carefully snipped a circular hole along the top to retain much of the strength of the thick plastic that the manufacturers used. It turned out really well, at least as an interim solution until I get a custom-fit media basket.
Bottle in place.
A view through the window on the back of the tank with the Nano-Glo on. I've since adjusted the height of the light and the bottle so it hits the algae more directly.
With the skimmer in place, the drip tray that had previously taken up all of the top of chamber two had to be cut down to size. I tried several versions of this reduced form and finally settled on cutting the thing entirely in half, also removing the raised plastic in the middle so that the filter floss would sit lower in the flow of water from chamber 1. As you can see in the pictures below, the glass side of chamber 2 (the back) did not have a support so I used one of the extra sucker pads from my Maxijet 1200 (the pump I use for water changes) to support it.
This set of modifications effectively provides the same mechanical filtration as I had before, keeps my chaetomorpha in one place, more effectively utilizes the light from the nano-glo, and makes room for the skimmer- which is an extremely useful means of removing tank pollutants and waste products before they even begin to decompose. I think a skimmer is probably the single best investment you can make with regards to water quality in a reef tank. Within a few hours it was already producing results:
All said and done, the corals and other livestock will be happier with the improvement in water quality, even though Zoanthids and some other LPS prefer to have some dissolved nutrients in the water; that shouldn't be a problem. The water is a already much clearer after only a few days of skimming and a healthy amount of frothing, bubbling spillover fills the collection cup with a tea colored cup of gunk every few days... gunk that would otherwise be floating around in the tank and yellowing my water.
I mounted two LED-based lights within the tank stand. It's much easier to work in there now, especially on any electrical wiring.
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