This article first appeared in the March 1990 issue of Aquarium Fish Magazine.
[1996: At the time I wrote this article, I was beginning to question the need for a trickle filter in reef aquaria. At the time, trickle filters were considered necessary components for success. Today we know differently and few people use them for reef tanks with live rock and lots of live coral.]
Glitter Lines: A Series on Reef Aquariums
by J. Charles Delbeek M.Sc. First off I would just like to clarify the title of this column, "Glitter Lines". Glitter lines are the bright lines one sees on the bottom of a pool on a sunny day, they are also common on the reef and in aquariums which use point-source lighting such as metal halides. They are caused by the refraction of light created by wave chop at the surface. Glitter lines can act as miniature magnifying lenses, concentrating the light on corals and algae as they pass over them. It is hoped that this column will serve a similar purpose. By concentrating and focusing on the important concepts of reef aquarium keeping, I hope to increase your knowledge and understanding of these beautiful systems.Part 2: Filtration
As in conventional marine aquariums, filtration in reef aquariums consists of three main types: mechanical, biological and chemical. The difference lies in how they are incorporated and utilized in a reef tank. Mechanical filtration is usually accomplished by an inert filter pad, biological filtration is provided by a trickle filter and chemical filtration can consist of various gadgets and substances to remove dissolved chemicals from the water.Mechanical Filtration
The main function of a mechanical filter is to remove large particles from the water BEFORE they begin to decay. This helps to reduce the amount of ammonia and other substances released into the water. The key to maintaining and designing a proper mechanical filter lies in regular cleaning. The easier it is to clean, the more likely you are to clean it on a regular basis. Frequent cleaning of the prefilter helps also to maintain a higher redox potential (Paletta, 1989) which is one of the keys in preventing hair and slime algae problems. Commonly used materials in mechanical filters include sponge pads and fibrous mats. One of the advents of the European philosophy which has gained prominence in North America, is the concept of surface skimming. This is the process where water is removed from the aquarium via the surface, resulting in a clean, clear water surface which enhances gas exchange and light penetration. Surface skimming is accomplished by the use of an overflow design which usually incorporates some form of mechanical filtration. Early designs consisted of an overflow located in one corner of the aquarium. A stand pipe was fitted into a hole drilled into the bottom of the tank behind the overflow partition and some type of filter padding was wrapped around the pipe. A problem with this design is that the aquarium hood and/or lights have to be removed to get at the pad. Another problem occurs in tall aquariums when animals or pieces of equipment fall into the overflow which then become difficult to remove. Since such overflows are difficult to service, they tend to be neglected and gradually become clogged. One then sees overflows half filled with water circulating around a brown stained filter pad. Recently, units designed to hang on the side of the aquarium have come onto the market. Operated by a siphon, they obviate the need for drilling holes and allow one to easily convert an aquarium to surface skimming and a trickle filter. The prefilter is then situated either in the overflow box or in the top half of the trickle filter and can be easily cleaned without disturbing the main tank. However, siphon boxes are not without their own problems. If they become clogged your tank may overflow onto the floor. If you change water pumps you should check first to see if your siphon can handle the new flow rate. Poorly designed units may also lose their siphon when disturbed.Biological Filtration
As I mentioned in my last column, the type of filtration used in a reef tank can differ greatly and is not, by itself, a characteristic component of a reef system. However, it is my personal belief that the use of a wet/dry or trickle filter, as the sole biological filter, is an important ingredient towards the success of any FIRST-TIME reef hobbyist. Although some people maintain that you can keep a reef tank with a standard filtration setup consisting of an undergravel filter (UGF) and an outside power filter (OPF), I feel that the limitations imposed by such equipment far outweigh any possible benefits. I would rather run a filterless (natural) system than use an UGF. Ok, so why am I against these filters, afterall they have served us well over the years? Ah yes, but think about it, have they really been all that good? One of the biggest problems in using an UGF is the thick layer of substrate required to support sufficient numbers of nitrifying bacteria. These are the bacteria that we depend on to convert toxic ammonia to less toxic nitrite which is, in turn, detoxified into nitrate. However, thick filter beds can become clogged by detritus and bacterial slime, and the amount of oxygen reaching the bacteria will become severely reduced. The pundits of UGF's recommend regular cleaning of the substrate to prevent clogging by detrital build-up. So there you are, siphon in hand, every few weeks stirring up your gravel, siphoning away the detritus, scaring the fish half to death and disturbing your biological filter. Imagine doing that in a reef tank filled with live rock, corals, anemones, algae and fish. As Thiel (1988) correctly pointed out, the more unpleasant or difficult something is to do, the less likely it is that you will do it. So eventually you become lazy and start neglecting your UGF. Detritus begins to build-up, the nutrient level of your water will increase, the mineralizing and nitrifying bacteria consume oxygen, the dissolved oxygen content of the water will fall and anaerobic areas may develop in the substrate. With a thick substrate (3 inches; 7.5 cm as recommended by most authors) the amount of oxygen which reaches the lower levels may eventually become insufficient and the area where the oxygen level is greatest, (the upper layer) is exposed to the bright lights of the aquarium which will inhibit nitrification. Furthermore, the substrate often recommended for use in marine tanks is crushed coral, oyster-shell, dolomite or calcite. The mistaken belief is that these materials will buffer your water and prevent the pH from falling below ideal levels. While this may be true for fish only aquariums, where it is not critical to maintain the pH above 8.0, it is not true for a reef system. The problem is these substrates will actually lower the pH to below 8.0, which is unacceptable in systems with invertebrates. They will, however, prevent the pH from falling below 7.6. Nevertheless, the substrate grains soon become coated with a substance which prevents it from reacting with the water rendering it effectively useless as a buffer anyway (Moe, 1989; Spotte, 1979). When this point is reached, the pH can be maintained above 8.0 with greater ease. Finally, too many people tend to rely on UGFs as mechanical filters and their nitrifying capabilities become severely restricted as a result.Trickle Filters
The concept of the trickle filter is not really as new to the aquarium hobby as some would have you believe. Early designs were outlined in popular literature in the 1970's (Siddall, 1977; deGraaf, 1979). However, it was not until the articles by George Smit, a Dutch hobbyist, were published in Freshwater and Marine Aquarium magazine in January 1986, that they became widely used in North America. Similar filters had already proved their superiority in Europe 10 years earlier and they have been widely used in aquaculture and public aquariums. The National Aquarium of Baltimore uses trickle filters on the majority of their aquariums, including their 250,000 gal Atlantic reef display. The main advantage of a trickle filter is it's ability to fully oxygenate water without the chance of anaerobic areas developing. A trickle filter consists of a chamber through which water is allowed to fall over some type of medium. The medium causes the water to spread out and cascade downwards to finally collect in another chamber (the sump) below the trickle filter from where it is pumped back to the aquarium. The medium of the trickle filter is not submerged in water but the water is merely allowed to fall through it. The term dry filter has also been used to describe this chamber, mainly to highlight the fact that the media are not submerged. As the water flows through the trickle filter, a thin layer of water covers each particle of the media, resulting in a very thin barrier across which oxygen can easily diffuse. This allows for a more thorough gas exchange between the oxygen hungry nitrifying bacteria living on the surfaces of the media and the atmosphere. Of course the opposite occurs too, as excess carbon dioxide and nitrogen can easily be expelled from the water. In fact trickle filters used in water purification and aquaculture are often called degassing columns. The result of this gas exchange is a very large population of aerobic nitrifying bacteria with no possibility of the formation of anaerobic areas. As long as the prefilter is performing its function, a properly designed trickle filter should never have to be cleaned. Water is delivered to the trickle filter by one of two methods. Either via a rotating spray bar or through a plate in which numerous small holes have been drilled, commonly known as a drip plate. There seems to be some debate about the merits of each to which I would like to add my own observations. The argument against the use of spray bars focuses on the belief that they drive out carbon dioxide and other gases, resulting in a shortage of carbon dioxide for plant growth. However, it seems to me that a properly vented trickle filter will do much the same. Spray bars are also vulnerable to clogging by detritus or other matter which may escape the prefilter such as may occur when you are cleaning the prefilter pad and a precocious 2 year old dumps his/her gum down the overflow pipe while your back is turned! In addition, slime can build up on the internal plastic surfaces further reducing water flow. Finally, poorly designed and/or constructed spray bars often stop rotating resulting in very poor water distribution. This tends to go unnoticed, especially if your filter is located in a cabinet below the tank. The supporters of spray bars advocate their superiority of water dispersal over a drip plate. In my mind there is no real difference between the dispersal abilities of a spray bar and a properly designed drip plate. Rotating spray bars are used in sewage treatment plants to allow a short drying period of the media as the bar slowly rotates. The small size of hobbyist units and the high speed of rotation of most spray bars prevents this type of advantage. If you use a rotating spray bar make sure that it is not rotating too rapidly or you will end up spraying the majority of the water against the sides of the filter and it will by-pass the majority of your media. The most commonly heard complaint about drip plates is that they can clog. To my mind this is not a very sound argument for the following reasons. First of all the number of holes in a drip plate are far greater than in a spray bar and the chances of them all clogging to the point of severely restricting water flow seems slim at best. Secondly, it is a simple matter to incorporate an overflow pipe in the drip plate such that an unusual increase in water level can be easily by-passed into the trickle filter or sump. Lastly, if your prefilter is functioning properly nothing large enough to clog a drip plate severely should get through. On the off chance that it might (remember that 2 year old), it would be a simple matter to remove the top of the trickle filter and take out the offending object. My own filter has a drip plate, for the very simple reason that it was much easier for me to make than a rotating spray bar! The media used in trickle filters has undergone an amazing explosion of variety and claims as to the relative merits of each. When they first appeared on the market in 1986, commercial units utilized a roll of double layered spiral (DLS) material in the trickle filter. Although DLS is still available (and I might add, has been used successfully by many hobbyists), there are now various balls, rings, blocks and several media previously used only in the water treatment industry. It seems that almost every month a new media appears along with various claims as to its efficiency and superiority over other media. In the end there are really only two main factors which are important: usable surface area and void space (Moe, 1989). The amount of surface area available to bacteria can sometimes be much less than that claimed by advertisements. Obviously the greater the available surface area, the more bacteria that can be grown and the greater the nitrifying ability of the filter. One way that manufacturers use to increase the surface area is to decrease the size of the media and to increase the number of protrusions such as ridges, bars, rods and bumps. While this can be a positive thing, if taken too far, other problems can occur. This leads us to void space, which is basically the amount of empty space available in a trickle filter after the media has been added. Void space is important for gas exchange and to prevent clogging of the media by detritus or bacterial slime. If the media is too densely packed, then there will be a low void space and a large surface area. While this may be good for nitrification it is not a good situation for gas exchange and clogging of the media can become a problem. If the media is too loosely packed you will have a large void space and a low surface area. Again, although this may be ideal for gas exchange it is not the best situation for nitrifying bacteria. The best media would be the one that could give you greatest amount of surface area without decreasing the amount of available void space significantly. I personally feel that, in reef tanks using live rock, the issue of whose media has the greatest surface area is a little overblown. In fact, many tanks have been run quite successfully without a large trickle filter, relying instead on the bacterial population of the rock and the associated algal growth to deal with nitrogenous wastes. In my view, the most important function of a trickle filter in a reef tank is gas exchange and not its nitrifying ability; that is secondary. There are various styles of trickle filters, however, most of them lack any originality, despite their rather exaggerated claims. Early versions employed removable trays on which a calcareous filtrant was placed. Commercial units soon turned away from this design favouring instead a tower design for the trickle filter containing an inert medium, located above a sump. The sump contains various chambers for chemical filtrants and the return to the tank. Other units contain various accessories located in the sump such as skimmers, probe holders, float switches and water level sensors. The latest craze is a trickle filter, run by a power head, which can be hung on the back of the tank. Although these units appear to be ideal at first glance, most of them have no provision for adding any type of chemical filtration. In other units the drip plate is poorly designed and water does not flow evenly across it resulting in an uneven water distribution. In still others, air injection into the dry chamber is difficult at best, the volume of the dry chamber may not be suitable for the size of aquarium it is used with, the flow rate through the filter is inadequate (too fast or too slow) and the trickle filter is not shielded from the light in order to aid bacterial activity and retard microalgae growth.What to Look for in a Trickle FIlter
With the recent explosion of reef system popularity, it is hardly surprising that it has been equaled by a simultaneous explosion in the number of available filters. Unfortunately, the number of fly-by-night operators and shoddy filters has also increased. I will offer a few suggestions as to what to look for when buying a trickle filter but ultimately the responsibility for your purchase lies with you so maintain a skeptical attitude towards any manufacturer. Pay more attention to the design, materials, construction and their business track record, and less attention to their advertising hype. First of all try and get a look at a running version of the system you want to buy, don't rely on photographs. Most systems look great while they're new and shiny, but only after they have been running for a few months will design flaws begin to become apparent. For example, unless taken into consideration during the design phase, salt creep and spray can occur quite easily in a poorly designed trickle filter. Unless you have seen the filter in operation you may not realize this until its too late. Take a good look at the quality of the material used in the construction of the filter. Pay close attention to the joints and seams. Are there any air bubbles present? Are the joints mounted flush or are there protruding edges? Have the saw cuts be cleaned and sanded properly or are jagged lines clearly visible? Has the filter been cleaned and polished appropriately (if acrylic)? These are just a few of the things you should be looking for when checking out a filter. By paying close attention to such details it shows that the manufacturer puts a lot of work into their product and are justifiably proud of their product. Whenever a pump shuts off in a trickle filter, water continues to flow into the sump for a few minutes. Unless the sump is an adequate size for the tank it is running on, you will flood the floor very quickly. Make sure that the sump of the filter you are considering has a sufficient volume for the size of tank you will have it hooked up to. A large sump also provides an adequate reservoir for the pump to draw from, preventing it from running dry quickly due to evaporation. If you want to add some sort of chemical filtrant to the sump, you will need a chamber built into the sump for such an addition; the same applies to the addition of probes and/or float switches. Check the method of water dispersal used in the dry portion. Does the filter use a drip plate or a spray bar? If it uses a drip plate, is there any provision made for the possibility of clogging of the plate? In the case of a spray bar, seeing one in action speaks volumes on its dependability. Poorly designed spray bars stop rotating quite easily. There are many other additions to a trickle filter that can show you that some thought and care has gone into its design. For example, the addition of an air injection fitting into the dry chamber makes it easy to add air to the trickle media chamber of the filter (which is highly recommended to increase the supply of oxygen to the bacteria). Brackets for holding probes are also a nice option. Some units are available that include a float switch that can be used for adding top- off water, another nice touch. The quality of fittings provided (some manufacturers don't provide them; a cost cutting move) with the filter is often a good indication of the reliability and knowledge of the manufacturer. Some fittings can contain materials that will not stand up under continuous submergence in salt water or to the affects of ozone. The quality and depth of the installation manual (if provided) is another good indicator of the type of company you are dealing with. Finally check out the company who manufactures the filter. How long have they been in business? Will they provide you with references of previous customers? What kind of post-purchase support do they provide? Does anyone answer the phone when you call (although this may sound odd, many times you can never get an answer; not a good sign)? The last bit of advice I would add is that cheaper is not always better. Too many times I have heard how one place is a few dollars cheaper than another so the purchase was made there. No matter that the latter manufacturer had been in business for 5 years and had a good track record for support and quality. No, the filter was bought elsewhere simply because it was cheaper. Unfortunately, such filters end up costing more in add-ons, repairs and cleaning bills. The better filters are expensive because a lot of work has gone into their design and manufacture i.e hand polishing and flame polishing of acrylic filters. Not until an injection molded design appears will the price fall dramatically. Please folks, beware of bargain basement prices, chances are you will end up with a bargain basement filter that you will not be very happy with. Next time, we will take a look at chemical filtration, its importance and the various types available.References
deGraaf, F. 1981. Handboek Voor Het Tropisch Zeewateraquarium. A.J.G. Strengholt Boeken, Utrecht, The Netherlands. Moe, M. Jr. 1989. Marine Aquarium Reference: Systems and Invertebrates. Green Turtle Publ., Plantation, FL. Paletta, M. 1989. Suggestions for reef maintenance. Seascope Vol.6, Summer 1989. Siddall, S.E. 1977. Some design ideas. Mar. Aquar. Vol.8 No.5: 5-57. Spotte, S. 1979. Seawater Aquariums: The Captive Environment. J. Wiley & Sons, NY. Thiel, A. 1988. The Marine Fish and Invert Aquarium. Aardvark Press, Bridgeport, CT.