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Related FAQs: Rock and Wood in Aquascaping

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/The Aquarium Gardener Series:

Rock and Wood in Aquascaping

By Bob Fenner


What would a captive aquatic system without aquascaping? A water-filled box with at least one transparent viewing panel? Or, consider if decor possibilities were confined to "novelty" ornaments. How many burping clams/ceramic castle/plastic plant themes can you and your livestock take? Thank goodness for the abundance of natural materials available and suitable for aquascaping. These serve many useful and aesthetic purposes; breaking up the environment, providing nooks and crannies for forage, escape and other "natural" (there's that adverb again) behavior.

Unfortunately, as with other aspects of our hobby, there is a potential downside to what is offered in the trade and collecting your own aquarium embellishments. Much of what you can get is not a good idea, due to toxic interaction with your water and its inhabitants.

Toxic Aquarium Decor Syndrome:

Ideally, what you place in a system should either do nothing deleterious to alter its chemistry and physics, or alternatively, be entirely inert (non-reactive). How many us want to understand how, what and to what extent a rock, piece of wood, et al. are contributing to hardness, pH shift, specific gravity, ad nauseum? We'd be happy to know that whatever's in "there" is either contributing to the overall health of the system, or at least not outright poisoning the inhabitants.

A counterbalancing point I want to make is that everything changes, including what goes on in captive aquatic systems; there is no null hypothesis. In the wild, some cichlids 'eat' rock material and Loricariids (South American sucker-mouth catfishes) ingest large quantities of wood, reductive processes shift pH, wood decays, rocks melt. Natural systems and aquaria have buffering and counteracting influences in constant interaction, physically, chemically and biologically.

Your job as keeper of these kingdoms is to master my favored oxymoron, "dynamic equilibrium". To keep this ever-changing world balance-shifted in favor of its desired habitants.

The or At Least A Test for Safety:

The modern world of physical and chemical assays is amazing. There are contraptions of sophistication that can analyze a substance as to it's mixed makeup to parts per trillion and smaller. These are so far the domain of physics, physical chemistry and government-subsidized (i.e. hopelessly money-losing) laboratories, not pet-fish hobbyists.

True, there are general assays mere citizens (the ones getting robbed by the above labs) may pursue. Placing a drop of an acid or base on the subject matter to check if it's reactive in the grossest sense could grant you some relative awareness (compared with other specimens that don't react?), but, really, what's the sense? I mean, do you thereby know whether the material is safe to put in your tanks? Ah, but there is a way to be sure.

Bioassay is the name given to testing formats involving live organisms exposed to questionable matter under set regimes. This is the realm of science: testable, falsifiable hypotheses. That is, designing and executing experiments under controlled conditions in attempts to disprove a state-able, somehow observable event. By such real means I can assure you that drip-tray methods of delivering water to wet-dry filters are superior to spray-bar technologies, that the vast majority of marine organisms from the Philippines are not cyanided,... Other ways of "knowing" such as faith, intuition, anecdotal evidence are valid, but are not science and of limited value to the serious aquarist.

The science of bioassay you want to engage here is simple and straightforward. By exposing some test species (singular/plural) to the proposed decor we will be able to make some decision about whether to use it in our display system. A word of caution here; there are two relative terms of degree we need to define, chronic and acute. Just how much, how fast does poisoning have to occur to be considered "acute"? Or, more meaningfully, how little does something have to act as a toxicant before we say it has no chronic poisoning effect?

For our purposes here, let's agree that acute refers to situations that result, directly or not, in losses within 24 hours, and chronic we'll give a month. Notice how arbitrary these values are, and further and more importantly that poisoning or lack thereof is not defined as any successive loss of vitality other than the threshold of death.

Useful examples of the above descriptions might involve the effects of ammoniated cleaners being used around aquaria for acute, and placement of geodes in a soft-water system for chronic poisoning.

A proposed bioassay approach for testing potential decor items is to "lightly" (about a minute) boil a sample of the material in the type of water to be used in the system, allow all to cool, place item(s) and water into a bowl or small tank, and introduce "test" organisms. What sort of "guinea-pigs" should you employ? If your intended use is for a fish, invertebrate, plant system, probably some of all these. Be wary of utilizing the (to some) lowly comet goldfish for all freshwater trials; after putting up with humans for a few hundred generations, this di-hybrid is too tolerant for all but general purposes.

If/when the test organisms have lived apparently none the worse for wear, for two or more weeks, the decor can probably be considered "safe" for use.

Another (Physical) Concern: 

Separate from considerations of what rock and wood, etcetera might and will do to your water is the question of mechanical danger. Maybe that coral, shell, colored glass has been sealed up, otherwise found to be rendered chemically inert, but what about cuts and punctures? Though aquatic organisms look supremely dexterous, they and you will get gouged with sharp, piercing edges and projections if such fare is handled or placed carelessly. Keep sharp objects away from dull livestock. Enough said?


There are many. Despite the paranoia this article might seem to inspire, rock and wood material abounds that is of use in aquaria. Your local and not-so nearby wholesale and retail pet-trade contacts are apparent; but so are sand and gravel plants, masonry and landscape suppliers. And, how about collecting your own?

A note of caution about the last possibility. Be especially careful with materials brought in from the "wild", even ones collected underwater. Though you might clean, bleach, dechlorinate, and dry your heart out, these can still turn out to be more trouble than they are worth. When in doubt, leave them out. For cost and space reasons, many outlets don't carry much of what's available through the trade. There are wonderful woods (pre-cleaned and sinking) that they can order from the U.S., Far East and Africa. Ask your source to check with their suppliers and special order your show pieces. You would gasp to see a whole cargo container load.

A Weighty Matter: 

What weighs more a pound of fish or a pound of feathers? They're the same. Now, which is more dense, as in density equals mass over volume? The fish, of course. Perhaps surprisingly, some rock and most wood needs be made more dense to be of use to us as aquarists. This can be accomplished either by fastening or adding to the material to something dense and massive enough to keep it down. Towards this ends there are silicon rubber (Silastic tm), epoxies and some ceramics that are suitably inert after curing. Obviously the finished product(s) of all this improvement should be tested as to the subject decor itself.

It's A Beauty, eh?

No discussion of aquascaping would be complete without at least a brief mention of aesthetic elements. You have all this stuff, now how do you put it together so it looks good? As any sensible person who has been on a date, entered or judged at a fish show will assure you, "Beauty is (indeed) in the eye of the beholder". After attending many exhibitions, reviewing the whys and wherefores of the "winners" and, more importantly, diving around the world seeing habitats first hand, the following "guidelines" vis a vis aquarium beauty are offered:

1) Balanced is Unbalanced: 

Symmetry, as in bilateral (mirror image) penta (like starfish) -ramous or otherwise is not natural, or attractive. Take a look around you nature-wise; non-symmetry rules, and it's beautiful. Don't evenly space the elements in your environment like a robot.

2) Points of interest:

Most humans "appreciate" a given view from the top left to the lower right. touching on the above 'balance' idea, you do want to capitalize on the non-equal opportunity you have to control the appearance of the system "frame". For smaller systems this translates into a small odd number (3,5,7) of highlights (vertical, horizontal, fore/background, size/shape, color, texture...) arranged to 'guide the eyes'.

3) Harmony, or better still "Telling A Story" 

Is a worthy quality to pursue. Whether a biotopic slice of real habitat is your goal, or some other-worldly vision, the tanks arrangement can and should be an attempt at completing this whole; i.e. making a discernible statement.

These are only my three favorite notions of what to shoot for in the way of aquarium beauty. Judging sheets and discussions with other aquarists reveal as many different values and weighting as queries themselves. So goes another footnote on the subjectivity of reality.


Have you ever wondered just how safe the resins used to make decor are for your fishes? Do the lead weights used with aquarium plants release metal into their surrounding water? What are the effects of lower pH, temperature, softened water, et al. on the solubility and toxicity of whatever finds its way into your systems? How much should you be concerned?

Going to all the trouble and expense to provide initially "clean" water, avoiding excess nutrients through careful chemical use, conscientious feeding, adequate filtration and water change practices is easily negated by haphazardly placing soluble, toxic rock, wood and other ornament in your system. A word to the wise; don't count on your sources to ascertain whether what they offer is toxic or not; test it yourself with a simple bioassay.


References/Further Reading:

Fenner, Bob, 1992. Aquatic Environments, Aquarium Ornaments: Rock & Coral. FAMA 4/92.

Fox, Timothy R., Aquarium Decorations, Hitting Rock Bottom Can Be Profitable. The Pet Dealer 8/92.

Osborne, Kevin, 1983. Esthetic Elements of the Planted Aquarium. FAMA 10/83.

Wholesale Sources of Rock and Wood for Aquaria

Aquarium Systems, Inc.8141 Tyler Blvd. Mentor, OH 44060,216-255-1997. Original distributor of 'p.c.' naturalistic ornaments.

Dolphin International1125 W. Hillcrest Blvd., Inglewood, CA 310-776-2352. Worlds largest pet livestock distributor; have
nice wood seasonally.

Feller Stone, Inc.1051 N. 1100 W. St. George UT 84770, 800-776-2206. Leaders, originators of modern natural aquarium decor industry.

Oceanic Systems, Inc. 11839 Shiloh Rd. Dallas, TX 75228, 214-320-6050. Have some really neat artificial coral art.

Tetra Second Nature and Terrafauna, 3001 Commerce St., Blacksburg, VA 24060, 800-564-3711. "Aquarium Correct" decor and so much more.

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