When looking at trickle filters, the first step in the decision process should not be which filter to buy, but what quantity of medium does the filter need to contain. To be able to determine that number you must first know how much biological surface area will be required to run your tank successfully. Each and every tank is different in this respect. The amount of surface area needed is directly and highly related to the type of tank, how much the biological load is, what type of filtration you will be using, whether or not you will install a protein skimmer, whether or not you will be using ozone, whether you use activated carbon, chemical filtration methods etc.

It certainly is not as simple as some would like you to believe when making recommendations such as: use 10, or some similar number, percent of the water content of your tank, in equivalent gallons of biological filtering medium.

For example: for a 100 gallon tank such recommendations often state that you must use 10 gallons of medium. Now I ask you: what medium? Why 10 percent? Why does this percentage apply to all aquariums uniformly?

What about aquarium loads, types of filtration used, skimmers, ozone, etc. I can honestly not accept such generalized recommendations because they are much too all-encompassing and comprehensive. Moreover, my long experience in running salt water and reef tanks tells me that such recommendations are inaccurate, and always result in filters that hold much more material than is necessary, or hold the wrong type of material, because hobbyists have not paid attention to the suggestions made earlier in chapter 3.4.2 in this book, specifically with regard to the qualities that such media should demonstrate to be efficient in the long run.

This is, unfortunately, compounded by the lack of knowledge regarding trickle filters in general and their required features in particular, and results in hobbyists often ending up with not only the wrong filter, but the wrong filter with the wrong biological filtering medium inside. Not a rosy picture of course.

The more the hobbyist "knows", therefore, the better off he or she will be. Buying as an educated consumer in a market place that, for the time being, is still full of hearsay recommendations rather than true empiric evidence and real requirements is, as a result, a must. At least for a while to come, until such time as acceptable practices for keeping reef tanks become better and better known and acknowledged by pet store owners and personnel.

Reading a lot, and asking many questions is the only way for the hobbyist to protect him, or herself. In this still very much evolving environment, where a lot of untruths circulate in pet stores, articles in magazines and in aquarium society circles, the hobbyist must be aware that his or her own knowledge is paramount to getting the right product for the job at hand. But such is the fate of any new method or practice. It is, fortunately, not something unique to the aquarium hobby. It is also not something that we should commiserate about but simply be aware of and take into account when making purchase decisions. As time goes on, and as successive printings of this book come to the market, we will, hopefully, be able to remove this section entirely soon.

Having said all this, what type of surface area should the hobbyist then be looking for, especially since this is the first thing one needs to know before being able to decide on the actual medium and the size of the filter? As is so often the case in matters relating to aquariums, there is not one single answer. This is so for a very good reason: aquariums differ in the amount of livestock that hobbyists place in them, in the type of other equipment that is used, in how they are cared for, fed, what additives are added and so on. All of these variables influence the amount of organic material that is present in the tank, and all those variables need to be taken into account when establishing filtration criteria.

In an effort to simplify the picture somewhat, tanks can in essence be divided into 3 main groups: low, medium and heavy loads, and each of these types sets its own filtration requirements:

• Low load tanks are defined as aquariums that are visibly low in life forms, for example less than 1 small to medium fish per 10 gallons of water. A small fish is defined here as the size of e.g. a 3 stripe damsel of the size usually found in pet shops: 1 to 1.5 inches in length. Medium is defined as the size of an average sized Centropyge Angelfish, e.g. usually 2.5 to 3.0 inches in length. Alternatively, low is defined as an aquarium that has no more than 1 invertebrate, e.g. Atlantic Pink tip anemone of size normally found in pet shops, per 10 gallons of water. Most tanks do not conform to this picture because, although they may start up that way, hobbyists keep adding and adding lifeforms as time goes on, never or hardly ever changing anything to the filtration.
• Medium load is defined here as the above type of fish and invertebrates per 5 gallons of water in the aquarium, or a mix of fish and invertebrates mentioned above, again per 5 gallons of water. Quite a number of hobbyists' tanks fit in this category. This is especially so for tanks owned by hobbyists who are aware that loading up the tank cannot go on forever when the basic filtration, the one that was installed when the tank was originally set up, is not changed.
• Heavy, or high, load is defined here as anything that is higher than the two categories described already. This definition probably places most hobbyists' tanks in the heavy load category. This is so because most hobbyists tend to keep on buying and buying fish and invertebrates, and eventually their tanks end up in the heavy load category.

If the latter is so, and if the hobbyist is realistic and willing to recognize that this is probably what he or she will end up doing, then such hobbyists should plan for this scenario. Perhaps not consciously so, but because each time the hobbyist goes to the pet store, and sees an animal that he or she likes, it gets brought home and added to the tank. Progressively the tank houses more and more lifeforms, and the system, the filtration that is, gets taxed more and more. Because, in my experience, this scenario is so typical, it makes sense to plan for it at the time the filtration is selected and purchased.

Experience is about all one can rely on to suggest adequate levels of surface area for biological filtration for each of these categories. There are no formulas one can work with, and there is no real scientific way (yet anyway) to determine such numbers. But experience is an excellent teacher and has demonstrated over the years that certain levels of surface area can cope with certain levels of biological load and certain aquarium practices.

Different authors may suggest more generalized numbers. Others may go into more detail. You may wish to refer, for example, to Martin Moe's The Marine Aquarium Reference - Systems and Invertebrates, for some additional insights. My suggestions for surface area in trickle filters using a plastic medium that fits the norms and criteria outlined before, are as follows:

• Low load: 0.95 to 1.50 square feet of surface area per gallon of water in the system (capacity of tank minus displacement by rocks, plus water in the sump.
• Medium load: 1.50 to 2.00 square feet of surface area per gallon of water in the system.
• High load: 2.00 to 2.50 square feet of surface area per gallon of water in the system.

Let's look at a few examples using the high load recommendations, as those are the ones that I feel most hobbyists need to provide for:

Tank size 55 gallons: 55 times 2.00 = 110 and 55 times 2.5 = 138 square feet of surface area. Using, for example, Bio Techs you would need between 5.00 and 6.27 gallons of Techs to run an efficient system. A filter holding 5 gallons of Bio Techs would be the right filter for you. An additional gallon to gallon and a quarter could be placed elsewhere in the system, e.g. in the overflow siphon or in a similar place.

Tank size 70 gallons: 70 x 2.00 = 140 and 70 x 2.5 = 175. Again, using Bio-Techs you would need 140: 22 or +/- 6.36 gallons to 175: 22 or +/- 8 gallons. In this particular case you may want to buy a 10 gallon capacity unit, even if you only place 7 or 8 gallons of plastic filtering material in it. You will have space and area to spare.

In the above examples we used Bio Techs. Using a different medium will, of course, yield different results. Using Super Techs, which have a larger surface area than Bio Techs, you would need less material, and you would end up needing a smaller filter in certain cases (numbers are averaged):

Use these numbers and examples only as guidelines. You must do a similar calculation for the type and size of tank that you plan to run yourself. The key, when calculating, is to use the exact surface area of the medium which, as already indicated, is not necessarily the one that you may see in advertising. If you overestimate the surface area you will not be using enough material. For the above calculations we have used the figures of 22 square feet for Bio Techs and 29 square feet for Super Techs. These are realistic linear surface area numbers, and are based on an as accurate as possible a calculation of surface as could be arrived at using mathematical modeling included in "Mathematica", a mathematics computer software program that is available for both IBM and MacIntosh type computers.

The previous six printings of _The Marine Fish and Invert Reef Aquarium_ listed different required surface areas. These numbers have been revised to take the most recent media surfaces into account, as well as more recent information on actual surface area needed to run an efficient system. The changes made are not very significant in nature however, at least not in the domain of gallons of media needed as a percent of the total amount of water in the system.

For illustrative purposes we are including the required surface area numbers chart as it appeared in the sixth printing. We suggest, nevertheless, that you now use the numbers that are part of the 7^th printing as the guideline in deciding the surface areas needed for your particular system, and not the ones of the sixth printing.

Martin Moe, in his new book mentioned earlier, lists recommended surface areas of 3 to 5 square feet per gallon of water, depending on load. Because that number is not qualified with what type of material they apply to, and because of Martin's large knowledge about marine tanks, his recommendations must be taken into consideration as well, particularly if you are using media that are different from the ones mentioned earlier in this chapter: Bio Techs and Super Techs. Incidentally, if you have not yet read his book, you must. His latest is also his greatest. Additionally he addresses a number of filtration techniques that are not included in this book, that are also to be considered.

You must keep in mind too, that after a short period of time anything in the aquarium acts as a settling place for bacteria. Rocks, dead coral, decorative pieces, crevices in rocks and decorations, the inside of pipes, the inside of ball and check valves, the siphon or overflow box that brings water down to the filter, glass or acrylic panes of the tank, etc. Bacteria do not know the difference and settle on any appropriate medium. What we are trying to do with a trickle filter, is not only to provide these bacteria with a large amount of surface area to settle on, but influence the area where this surface is in such a way, that it is more propitious for them to colonize, by increasing the amount of oxygen in that area, and keeping the settling medium out of the water. These two factors, combined, result in both a more powerful and more potent colony of Nitrobacter and Nitrosomonas bacteria, which in turn bring about better water quality in the tank. Because the area is favorable to their growth, large amounts of bacteria will colonize it.

• To recap: First determine the amount of surface area that you will need for the type of tank you are installing, then select a medium, using the remarks made in this chapter as a guideline, and find out its exact surface area per gallon/volume, now calculate how may gallons you will need of that material, and then decide what capacity your filter should have. Take the recommendations made with regard to desirable options and features into account.

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