Skip to content

Reefs.org: Where Reefkeeping Begins on the Internet

Sections
Personal tools
You are here: Home » Library » Aquarium.Net Article Index » 0397 » Aquarium.Net March 97

Aquarium.Net March 97

Sam Gamble continues his monthly articles on sand bed fitration, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

Sugar Sand

by Sam Gamble

In the last article some of the problems that can occur from less than optimum sand were discussed. I mentioned that this month would deal with some of the problems animals can cause. However, I would like to postpone that topic for another that has recently been gaining interest. That is the use of finer grain size, as some refer to it as "sugar sand", for their passive filtration.

First of all some hobbyists prefer it, if for no other reason, than it looks more appealing to them. In one instance, it was reported to be more like what had been seen on a reef while snorkeling. Reef sand varies as greatly as the reefs do. The type of sand will be different at one location on a reef as another. So what "reef sand" typically looks like is a judgment call for a particular reef and what part of the reef is used as the example.

Since the reefs vary as do the quantity and quality of sand associated with them, the important factor is what they do in closed system aquariums. The bottom line is to achieve water quality that is acceptable for the survival of the organisms you choose to maintain. It's perhaps obvious that your aquarium must match the filtering capacity to what is in the aquarium for survival. The fine grain sand has been an interesting variation to the sand bed filtration method. It appears, that in some applications a successful one. Perhaps not without qualification.

The center of any filtration system is bacterial abundance. This arbitrarily overlooks qualitative descriptions of the microbes for the moment, but let's first look the ways quantitative factors occur.

There is a positive relationship between bacterial abundance and specific surface area. It is also well established that microbial activity can be enhanced by interfaces. It has long been commonly thought that smaller grain size and abundant microbial populations were a direct relationship, i.e. more surface area equals more bacteria. Which is largely true, but other factors contribute.

Other factors that have also shown to be important are;

  1. 1. Space for bacterial attachment
  2. 2. Environmental temperature
  3. 3. Distribution of surface area - sub rounded and sub angular being the highest.

Bacteria use only a small percentage of the surface area, choosing to concentrate in cracks and crevices, where abrasion is perhaps reduced. Variation in organic content may be more important than particle size in determining bacterial abundance. It's been shown that bacterial abundance in marine sediments correlates inversely with sediment grade, but correlated directly with carbon and nitrogen contents independent of grain size.

When fine grain size sand has been used in aquariums, there has been a consensus that there are physical advantages like simplicity of not using a plenum and the need for less sand. As for the filtering capacity of the sand, there has been little reported difference in parameters like nitrate.

I approached Rick Greenfield of CaribSea and his reply was supportive and interesting; "We have offered oolitic sand for about 6 months now as a product we named Aragamax. I think you will find it is cleaner, metal free, and a better color than the ESV product which is material diverted from an industrial application. Our two main selling points are the the two you mentioned i.e. a shallower bed is required to reach oxygen depletion and it truly is better for sand sifting benthics. It is the overall performance aspects which I believe are going to differ.

One thing that I have noticed is that our oolitic sand (Aragamax) works well for people who don't really want to change their philosophy of reef keeping from primary reliance on manual manipulation of water parameters. Oolitic sand has no downside if it is never expected to control water chemistry. Simple denitrification in an established reef system is not a tall order for a substrate. I don't expect oolites to measure up to the performance of special grade reef sand outside of the two circumstances mentioned above. In the more demanding conditions imposed by beginners, all natural reef systems, commercial applications (heavy, fluctuating bioloads with little chemical help and lower filtration) and the heavy bio-mineral demands of some reef systems, I still think that reef sand is the way to go.

I don't think there is any truth to the assertion that oolitic sand dissolves much faster, or even faster, than say, special grade reef sand. It seems to make sense that oolitic sand would dissolve faster if you look at it by purely surface area considerations as oolitic sand has a smaller grain size (ignoring pore water considerations). However, under an electron microscope things look a lot different. Oolitic sand is a dense, smooth, spherical grain while the majority of our reef sand is Halimeda segments, which appear like fiberglass mat under relatively low magnification and a forest of needles at higher power. Add to this the familiarity of dissolution rates to marine geologists who seem to prefer Halimeda in practice.

All this being said, it's still a judgment call."

The main event in the aquarium - is filtration. To have the optimum qualitative and quantitative bacterial populations is paramount. The factors controlling bacterial abundance in marine sediments are complex. Studies suggest that bacterial abundance is the result of density-dependent processes which are in turn regulated by particle surface area. Even though particle surface area may not be the primary factor involved in determining bacterial numbers, it appears that most of the controlling factors have some areal dimensions. Other physical factors, such as the three dimensional arrangement of particles, the topography of individual grains, and the distance between particles as a result of packing seem secondary.

The application of field studies to aquariums must be interpreted with caution. As much as we try to copy all the best resources nature has to offer, we still produce artificial differences. This may be part of what Rick refers to when he mentions overall performance. Environmental variances we cause are things like;

  1. Constant temperature, without seasonal change.
  2. Relatively constant sources of nutrient enrichment either by feeding (like with fish) and/or limited space (like volume of water).
  3. Incomplete spectrum of benthic fauna and infauna
  4. Difference in current abrasion and turbation. to name a few.

Protein may play an important role in this. It may be manifest by systems with or without foam fractionators. Protein-enriched substrate samples have consistently higher bacterial abundance than those not enriched. Adsorbed protein could be important for the growth of bacteria as a nutrient and energy source. Protein as a renewable nitrogen source encounters loss in recycling, while as an energy source it is not renewable.

Protein may also serve as a substratum for bacterial attachment. Since most surfaces in nature are negatively charged and most marine bacteria are also negatively charged, electrostatic forces would probably make it difficult for the bacteria to attach directly to particle surfaces.

Sand sifting benthics may have easier going with a smaller grain sand. However, are they getting more of what they need? From the standpoint of a deposit-feeder, the optimum for getting the most bacterial nutrition is quite complicated. If the animal chooses only the surface rich area of sand, it is not necessarily getting the most bacteria-rich fraction, although the selection of a bulk sediment rich in surface area would likely contain a high bacterial population. Even though bacteria might not be associated with the surface-rich fraction, it is clear that absorbed organics are concentrated there. Less clear is the concentration of organics in the other sand layers of a sand bed system with a plenum.

Aquarists have reported infauna in their anoxic plenums. They have also found elevated amount oforganic content in the sand layer adjacent to it. The effects of burrowing and feeding activities on bacterial distribution and abundance is one aspect of the bacteria-sediment interaction that needs to be further investigated. The choice of substrate and system design makes it more complex. The rewarding part is to see it work successfully.

I would like to request the assistance of the readers who have built and maintained sand bed systems with fine grain sand. I would enjoy learning more about these systems and how they are working out. It sounds as if perhaps the sand bed system could be changing or evolving. Please, if you have the time, drop me an e.mail.

Sam Gamble 102170.3150@compuserve.com

Created by liquid
Aquarium.Net
Last modified 2006-11-18 19:07
Advertisement