Easy Reefing

Most saltwater aquarium systems require external filtration. The primary purpose of filtering your aquarium’s water is to remove organic waste created in the system. While this is an essential part of maintaining an aquarium, many beginners are overwhelmed with the plethora of filtration choices available. This article explains the basics—only what you need to know to get started. Additional research will be necessary to decide what is best for your specific system.

Think of your saltwater system’s filtration as a point-of-use Brita filter installed on your kitchen sink. The overflow from your display tank is like the kitchen faucet which channels water into the filter housing or, in the case of your saltwater system, the sump (little more than an acrylic box resembling a fish tank or even an inexpensive plastic tub). In the same way that “cleaner” water comes out of your point-of-use filter mounted on the kitchen faucet, the water coming out of your sump is also of a higher quality if you have set the sump up properly.

The process is not magic. In the case of your point-of-use filter on the kitchen faucet, the water, once it enters the filter housing, moves through a multi-tiered filtration system. In this system, activated carbon, ion exchange resin and other filter media remove impurities, heavy metals and particulate matter from the tap water through both mechanical and chemical filtration. These impurities are then removed from the system altogether by cleaning or replacing the filter cartridge.

The aquarist also relies on mechanical and chemical filtration to improve water quality (most aquarists also rely on biological filtration, but that’s another article). The water entering the sump from the overflow is often run through a filter sock which effectively filters out the larger particulate waste. Next, in the simplest set-up, the water moves from the first chamber of the sump to a second chamber and, in the process, passes through one or more types of filter media. This filter media, at its most basic level, is simply a filter pad designed to trap particulate matter. Once the water has flowed into the second chamber of the sump, it is then pumped back to the display tank. In addition to a filter pad, a filter bag can be filled with a wide range of filter media (such as activated carbon) to address various water quality issues. Like the Brita filter, the waste is then permanently removed from the system by cleaning or replacing the filter media.

While the above set-up will improve water quality, most marine aquarists also rely on a protein skimmer. The protein skimmer is usually placed into the first chamber of the sump where it skims the water entering from the overflow (skimmers require their own dedicated pump to operate). Protein skimming removes dissolved organic nutrients from the water before those nutrients are broken down by bacteria. Because a protein skimmer removes organic nutrients, it is possible to overskim your system. As a result it is important to properly install, run and maintain your skimmer according to the manufacturer’s directions.

Calcium carbonate reactors have become a popular way of replacing the calcium and carbonate taken up by corals in the process of calcification.

In its most basic form, a calcium reactor is simply a container filled with calcium carbonate (CaCO3) media over which aquarium water is passed with the addition of carbon dioxide. Adding carbon dioxide lowers the pH of the water, making it acidic, and dissolving the calcium carbonate to provide the aquarium with calcium and alkalinity.

Fluidized reactors have become very popular in the last few years for reefkeeping. Historically fluidized reactors were used for biological filtration and typically filled with sand or some other inert media to promote the growth of beneficial bacteria to aid in the reduction of Ammonia to Nitrate via the Nitrogen fixation cycle. The fluidization of the media greatly increases the surface area of the media allowing for a greatly increased amount of these strains of organisms. In the reef aquarium however fluidized reactors are being used for chemical filtration instead of biological filtration.

Fluidization of media is a very simple and effective method to increase the surface area of a given substrate to increase the transfer rate between the liquid and solid phases. Typically the substrate is fluidized using a controlled velocity of fluid to convert the substrate from a solid state to a liquid like state. Fluidized beds have many advantages including high transfer rates when used for chemical filtration as well as huge surface areas when in use as a biological filter.

Fluidized reactors used for chemical filtration in reef tanks typically contain phosphate adsorbing media, either granular ferric oxide (GFO) or alumina oxide (AO). GFO is typically used however due to some risk of releasing aluminum back into the aquarium water when using AO based media. GFO based adsorbents such as Rowaphos or Phosban are very popular as they will remove both organic and inorganic phosphate from the aquaria at a very rapid rate. Some care must be taken to reduce phosphate levels at a slow controlled rate or rapid tissue necrosis (RTN) can occur. However if low phosphate levels are achieved in a reef aquarium it will help reduce nuisance algae, increase coral health, color, growth and improve the reef bioload. It is a goal in maintaining a reef tank to keep nutrient levels such as phosphates at or close to zero (0-undetectable).

Granular activated carbon (GAC) is widely used in fluidized reactors as well as Purigen which is a synthetic adsorbent which has similar affinities toward organics comparable to GAC. Purigen will not adsorb trace elements or other metals such as carbon does which may be a benefit when the goal is to reduce Nitrates in a reef tank.

Overall fluidized reactors can play an important role in the reef aquarium. Not necessarily by providing biological filtration but as a means to export unwanted chemical elements from the captive reef by the use of the different types of media available to the reef keeper.

Because the tank is exposed to air, and strong pumps are circulating the water throughout the filtering system (overflow pipes, drip plate, prefilter, and protein skimmer), you will get a significant amount of evaporation. In fact, the better your skimmer and the stronger your water pump (both desirable features), the more evaporation you will get. You will need to replace the evaporated water regularly. An important reminder for the new hobbyist is that the water evaporates, not the salt. Do not add salt mix with the make-up water. The result will be a higher salinity than is desirable.

Adding make-up water provides a good opportunity to replenish much-needed calcium, which gets depleted rapidly in an enclosed reef system. This vital element is used by virtually all living creatures. Some of it also gets removed by protein skimming. In my opinion the best calcium additive is “Kalkwasser,” which is calcium hydroxide. It is added on a regular basis by mixing it with the purified water being added to compensate for evaporation. These regular additions of calcium hydroxide also keep the pH elevated to the desired 8.2 to 8.4 level.

Kalkwasser is a German word. Literally, it means “lime water.” Kalkwasser is a trade name for calcium hydroxide. The terms “Kalkwasser,” “limewater,” and “calcium hydroxide” all mean the same thing in this hobby.

The water you use to replace what has evaporated will be called “make-up water.” It is extremely important to use purified tap water mixed with calcium hydroxide (a.k.a. Kalkwasser, a.k.a. limewater) for the make-up water! Do not, I repeat, do not, use regular tap water or anything else for make-up water! This is asking for trouble.

As I have stated from the beginning, nothing will ensure your success more than the quality of your water. Once you have made the investment of a water purifying system and have started the reef with purified tap water, the reef will be accustomed to that quality of water. It would be extremely foolish to try to cut corners here. This is the last place to skimp. In fact, it would be inviting disaster by possibly introducing impurities (metals, silicates, phosphates, etc.) that are harmful and troublesome (hard to remove) into the pristine environment that we have tried so hard to create.

Benefits of adding Kalkwasser:

You may be interested in why it is so important to add Kalkwasser. Some of the benefits are: It adds calcium that is needed by most of the creatures in the reef. It encourages the growth of pink and purple coralline algae. It keeps the pH elevated. By adding Kalkwasser on a regular basis (make-up water) and doing water changes every 2 to 3 weeks, I have found my pH to be consistently between 8.2 and 8.4. Keeping the pH at this level makes it less likely that micro-algae will become a problem. The reef just seems to love Kalkwasser. There are many more scientific and chemical reactions that are beneficial. Take my word for it: adding Kalkwasser on a regular basis is one of the most beneficial procedures for maintaining a healthy reef and desirable water chemistry.

Next to primary biological filtration, foam fractionating, better known as protein skimming, is the next most important aspect of any healthy marine system. Wow, pretty powerful statement, huh? Although there are systems that claim to be "skimmer-free", such as Dr. Jaubert's Live Sand Plenum System, for most of us DOC's (dissolved organic compounds), phenol oils, and other yellowing agents are a nuisance that only active protein skimming can eliminate. Before we jump into the subject matter any deeper, let's discuss how these devices work.

To be as unscientific and as clear as possible, let's simply say that the air bubbles inside the skimmer's body strip the water of undesirable waste by-products. How the bubbles accomplish this is a neat trick that needs some explanation. Ever blow bubbles as a kid? Remember all the rainbow colors on them? Just as the soap clung to the giant bubbles you were creating so too, does all the junk and other organic gunk in your aquarium water. Those pretty rainbow colors were the light refracting off the soap film...you could actually see it! In our skimmers, the bubbles are microscopic and the results can only be "seen" after they burst and deposit their "films" into the collection cup! No pretty rainbow of color here...nope. Only the vilest and nastiest looking sludge imaginable ride our skimmer's bubbles.

How does this happen? It was discovered long ago in waste treatment plants that by injecting high volumes of air bubbles into a column of waste water, the resulting effluent was purer and much cleaner than before. How could this be? Actually, quite simple. Surface tension. Surface tension? What's that? The interaction between the oxygen bubble and the surrounding water creates a kind of friction between the two. This friction in turn "charges" the molecules in the water.