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Sand Bed Sytems Aquarium.Net Jan 97

December 1996 Index for Aquarium Net, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist


Sand Bed Systems

By Sam Gamble


From the last article, we have begun to picture some of the microscopic events that control our aquarium. Our methods of investigation are to measure important indices and interpret the findings. Even with the aid of good data like pH, dissolved oxygen, and ORP, solving new problems that the ecology of the aquarium may have, can be frustrating and perplexing.

Historically the problem with the greatest track record is nuisance algae. So let's start there. The cause is simple actually; water (medium), strong light (source of radiant energy), and nutrients (food, a.k.a. more energy and building blocks). Many people have tried the frontal attack, using hand to hand combat (removing the junk by hand), or chemical warfare (removing the junk by absorbents and starving it out). At any rate, it often takes months to be successful. When we see it start to disappear, we figure our battle plan has worked. I would like to suggest there was more to it than that.

Usually our maintenance (holy wars) for algal mats begins when we start to see the preliminary little tufts starting to grow. Then it can quickly become an emergency situation. Essentially you are starting out a couple of steps behind mother nature. The contention is that mats effectively retain nutrients for potential use in biomass production as needed. Mats illustrate a nearly steady state condition. Enough nutrients are generated in the mat by oxidative processes over 24 hours, to fuel primary production during the day (photosynthesis, etc.). Then it takes only a SMALL additional external source recruited, to balance the small amount of carbon buried in the mat. Bottom line they are structured and suited to thrive in water depleted of basic nutrient elements. Worse yet, they can easily seed new areas. Once you see them, they are ready to maintain and spread themselves even in low nutrient conditions.

This is the scope of the primary problem with the nuisance algae when we start a new system. The microbes that will be the heart and soul of our filtration (cycling) reaches the steady state or balanced condition a bit more slowly than the more adapted mats (the problem). The metabolically diverse, autotrophs and heterotrophs play vital roles in the cycling and balance of marine organic and inorganic carbon and nitrogen. Daily turn over of carbon and nitrogen due to growth, reproduction, and death by these groups, represents by far the bulk of mediated carbon and nitrogen cycling. Also, the rest of the consortium of microbes are also vital cogs in cycling. Getting this scenario in place quickly will give biofilms and mats the necessary competition.

When nutrients are supplied at higher levels, mats can jump ahead in line until microbes can eventually dominate the use of nutrients. The process seems eternal sometimes. But generally, we are at fault from the beginning. One source is rocks.

How many can identify with starting their new sand bed system (SBS) with the rocks from a previous aquarium? Or an analogous situation; to buy rocks from your favorite store that has had them in the holding system for several months. And despite good water quality, perhaps the rocks have absorbed a sizable amount of nitrogen and phosphorous compounds. A large biomass that partially dies off is essentially the same thing. The situation sounds unavoidable. So what do you do?

[an error occurred while processing this directive] Light: There is the commonly used start up procedure to keep the lights off or raised to evade one of the necessary elements for algae; strong light. It works pretty well, but there are some side effects. The rocks will loose most of the other things that also need strong light. For example, you may loose some of the highly prized coralline algae. Which we pay a high price for, when purchasing the rocks in the first place. Much of the life that diminishes when the light is removed, does return, but not as "natural" looking as before.

Nutrients: The other method is a natural competition of sorts. When starting a new SBS, you cannot start with a desert. There are, and will have to be, nutrients to feed the growing microbial populations. Obviously, trying to keep it as low as possible works best. The nutrients that are present will effectively be handled quicker if the balanced consortium of microbes is quickly settling into the empty niches, that you have so purposefully provided with the constructed sand bed.

There are a few major keys to this protocol, but perhaps the most important in this case is the ratio of carbon to nitrogen. In coastal marine benthic environments the ratio of amounts of C:N is usually around 6:1. Okay, where can you find a carbon and nitrogen ratio test kit? No can do, but the concept is important.

When nutrients get out of hand, it is often the result of the N part of the ratio getting bigger. This leaves either reducing nitrogen or increasing carbon to again reach balance (equilibrium). In the past , the most common methods of reducing nitrogen compounds has meant removal with protein skimmers, chemical absorbents, water changes, and that sort of thing. Increasing carbon sources has in "specialized cases", meant adding things like alcohols and sugars. But, given the chance nature will do all of the above.

Nitrogen can be cycled by nitrogen fixation (constructed into NH3) and/or destructive routes like denitrification. Also, carbon is very importantly coupled to the process. Close by in the same neighborhood are the sulfur reducing bacteria, which are noted for carbon transitions.

During sulfate reduction, energy flow is decoupled from carbon cycling. About 75% of the energy content of the organic matter which is decomposed is transferred and stored in hydrogen sulfide. When the sulfide and other reduced sulfur compounds are later oxidized, this energy is released and used by other microbes close by.

The microbes associated with nitrogen, and carbon cycling plus concomitant carbon involvement with sulfur bacteria, dramatizes the importance of getting the starting "live sand" growing and colonizing. This includes the ecology typical of the water to sediment surficial interface. Just a bucket of sand won't help you here.

When the sand bed has been inoculated with a sufficient spectrum, the microbes will generally take care of nitrogen and carbon. Your goal is to see that the microbial growth rates are ahead of algal mat development. Sometimes you win and sometimes you loose.

The balance or equilibrium of the C:N ratio is important on many fronts, but another factor outside of these energy cycles is the more kinetic phosphorous. With regard to rocks, sand, and nuisance algae, it is more a physical action. Phosphorous compounds like phosphate in our aquariums, have a tendency to go in and out of solution and onto surfaces.

Over generalized perhaps, but when we see the red, brown, and green hairy or slimy stuff, it has something to do with phosphate being on or near the surface of the substrate. Phosphate in high concentrations in the water has the ability to precipitate. It chooses calcium carbonate surfaces as one of the favorites. Microbial mineralization is also a major source of phosphate at the sediment to water interface. The additional sources produce enough fertilizer for mat proliferation. It tips the scales too far in the nuisance algae's favor.

There are other factors, but attention to carbon, nitrogen, and phosphorous will be affective and enough to keep you busy.

Ultimately the problem stems from organic compounds. You've most likely read things about dissolved organic compounds (DOC) and particulate organic compounds (POC). There are a few others, but they are derivatives. These compounds can be added or hitch hike into your system. If your rocks have come from an aquarium that had a history of high nitrate or other nutrient problems, then you are going to have preliminary problems.

If you build the sand bed with sand of small grain size (less than 1mm.) and from a source that has a sizable organic content (beaches, shallow water,or estuaries), you will also have problems. This theoretically may also include the wrong spectrum of starter bacteria.

All of these factors essentially do what the algal mats dearly love. You're putting the competition on the bench and the algae on the field with the ball. Touchdown! Slowly the mats use up their stockpile of energy sources, while the microbial populations grow and function well enough to play a competitive game. In the meantime there is some tough maintenance. Lots of time outs.

In a stable and well constructed tank, most algae problems will straighten out. This automatically assumes nutrients are not outrageous and microbial populations are colonizing. However, because of their adaptive characteristics to achieve a steady state, primitive algae can easily dominate conditioned surfaces once they have a foothold.

Constructing the ecological environment for the SBS to be more competitive by tank friendly microbial populations, is a good line of defense. Poor quality live sand, and nutrient rich rock substrates are a big drawback to this aim and usually manifest algae problems. All too many of us have learned the hard way. Unfortunately, we are the cause and have merely shot ourselves in the foot, by overlooking basic concepts of energy cycling and what causes it to happen.

In the past obtaining a healthy and functional Nitrogen Cycle was the primary goal and maintenance centered around sustaining the microbes involved. Keeping the detritus to a minimum and enough turnover through the filter to feed the bacteria and scrub the water. Now, we are talking balance, steady state, and equilibria. We're adding new words and concepts to our aquariums to make them simpler and more efficient. Seems paradoxical doesn't it.

Next time let's return to the subject of sand and take a closer look at one of the other common mistakes when building the SBS; cheap - o sand. In doing so we will have to return to the concept of biogeochemical pathways as illustrated by information from benthic ecology.

Ideas & comments;

Sam Gamble 102170.3150@CompuServe

Created by liquid
Last modified 2006-11-18 15:17