In the first two articles in this series, I discussed some of the dissolved components, mostly trace metals, found in the water from a survey of 23 marine reef aquaria. I chose to examine these elements for two reasons: first, many reef aquarists seem very concerned, "obsessed" is not too strong a word, about trace elements in their systems and, second, the concentrations of these materials could be analyzed relatively inexpensively. I have shown that the concentrations of many of these elements in our reef tanks bear little similarity to what is found in natural sea water (NSW). Additionally, I have shown that many of these elements have distributions that are correlated with one another. After comparing these data with the composition of the artificial salt mixes as reported in the literature (Atkinson and Bingman, 1999), it is apparent that some of the odd, and relatively very high, concentrations are due to the initial mixtures of the artificial sea water that we use in our systems. Our systems are very dynamic, however, and after a very short period bear only a passing similarity to what is found in either natural or freshly mixed artificial sea water.

That our systems are dynamic and ever changing should come as no surprise to any reef aquarist. However, the magnitude of some of these changes is quite impressive and the speed with which the systems can accommodate change is truly awesome. Most, if not all of these changes, are mediated by the organisms in the reef aquaria, and probably the most important groups of organisms in this regard are the bacteria and algae found in the aquaria (Redfield, et al., 1963). Under appropriate conditions, various bacterial and algal species will have large populations in our systems, and they have the capability for rapid metabolically induced changes of the medium. In natural reefs, about 80 percent of the non-bacterial biomass is algal (Odum and Odum, 1955). Coral reefs are, in point of fact, algal reefs with a small animal component layered over them like the thin frosting on a cheap cake. It is likely in many of our aquarium systems that the algal component is equivalently abundant; algae grow on the surfaces of virtually everything in our tanks, as well as within the rocks, corals, and sediments. When we set up our aquaria, we are actually constructing algal culturing vessels of very good design. Of course, all aquarists, myself included, then gripe loudly and vociferously about the algae "taking over" our tanks. Yeah, right... The rapidity of algal growth is amazing, as demonstrated by the dinoflagellate or diatom blooms we have had at one time or another.

For most aquarists, an unforeseen or unexpected side effect of such rapid algal growth is a significant alteration of the water chemistry; as some elements vanish from solution, while the abundance of others is hardly changed. Of course, some of the animals alter the water chemistry as well, but probably most of the alteration comes from either algae or bacteria. Such rapid alterations of water chemistry are characteristic of these two groups in natural systems, and are not at all characteristic of animals. Most animals use relatively little in the way of dissolved materials, getting most of the chemicals they need from their food. One rather peculiar animal, the reef aquarist, however, does significantly alter the composition of the fluid in reef aquaria. Aquarists can change the water chemistry of their systems either actively or passively. In the former case, they may add or remove materials from the system. In the latter case, they may simply do nothing, and in so doing, abet the changes occurring due to the actions of the various organisms in the system.

Undoubtedly as well, there are many strictly non-biological chemical reactions occurring in our systems, but with few exceptions, such as the effects of lime water or added buffers, these are likely of lesser magnitude and importance than are the biologically mediated responses.

In an attempt to estimate some of the effects that aquarists have on their systems, I asked the participants of "The Tank Water Study" to provide me with a detailed list of foods they used and their feeding schedule. I also asked for data on water changes; both if they performed them, and if so, how much water was changed at each instance and how frequently these changes were accomplished. By examining the composition of the foods that go into the aquarium, as well as the frequency of water removal, I could, rather crudely, estimate some of the factors influencing the composition of the materials dissolved in the aquarium water.

The nutrient and trace element composition of the foods was estimated by calculating the mass of the food added and comparing the foods to compositions of comparable foods in what I call "The Food and Additive Study"(Shimek, 2001). To estimate the mass of food added to the aquarium, I had to convert from a number of different odd and wonderfully esoteric measurements into metric units (Table 1). Most marine animal and plant tissue has a specific gravity of close to one, and I assumed that one milliliter of the foods derived from such tissue weighed one gram. This will introduce some errors, as some foods are a bit denser. These foods will be undervalued with regard to their contribution.

For some foods there were no available comparable data, so I estimated their values by using a similar food. For example, for an addition of mysids, I used brine shrimp as a surrogate. Likewise, for most of the algae used by the aquarists in the study, there were no data available. I used the values for dried Nori (Porphyra spp.) as a surrogate. This may over-represent the contribution of those algae, as Nori is a very rich food source. A square inch of whichever algae were used was estimated to be equivalent to 0.25 g of Nori.

Every feeding regime noted by each hobbyist was different, somewhat inconsistent, and approximate. To be comparable, I needed to bring them to the same standard, so I divided my estimate of the amount of food added in one week by seven to give "Average Daily Ration." This measure was used in all comparisons, even though many aquarists did not feed on a daily basis. The data from these calculations were tabulated and graphically compared to the concentrations of the trace elements found in natural sea water (Figures 1a - 1f).

To estimate the effect of the added foods in the tank, I asked each participant to give their system's size in gallons, and then to estimate the total volume of the rockwork and the sand. I assumed that the rock and sand totally displaced water. This is patently false, there is pore water in any sediment bed and there is water inside of the rock. The volume of this "internal" water is difficult to measure and even harder to estimate. However, in both of these cases, exchange with the main water volume of the tank will be slow, and these areas may be considered to be effectively isolated from immediate changes. In any case, however, the amount of water in each system was probably somewhat underestimated, maybe by a factor of as much as twenty percent. Such a reduction has the effect of increasing the calculated concentrations (Table 2).

The composition of the material fed was estimated by multiplying the components of the average daily ration by data from "The Food and Additive Study" (Shimek, 2001). In some cases, I was able to use the data directly from that study, as some of the participants indicated that they used foods that were examined in that study. In other cases, I averaged the values for a given component of food. For example, to estimate what was in a "generic" flake food, I used the average of the dried prepared foods examined in "The Food and Additive Study" (Shimek, 2001). For each of the foods, values for about 30 elemental concentrations were estimated. These were summed over all the foods. This sum was "The Average Daily Food Ration (Table 3).

For each aquarium, the proportion that the average daily food ration contributed to a water volume equivalent to that system was calculated relative to the same NSW volume (Pilson, 1998) (Table 3). These data are rather interesting. The average DAILY food ration contains enough aluminum, if it were totally dissolved in the tank water, to raise the aluminum concentration of an average tank from zero to 1.572 times normal. It contains enough iron to raise the concentration of iron in an average tank from nothing to 35.141 times the level found in natural sea water. This bears repeating: each day, each aquarist, added enough iron to an average tank to raise the iron concentration to over 35 times the normal sea water concentration. And yet, the tank water contains no detectable iron (Shimek, 2002a, 2002b).