rock or gravel

Dear hobby:

As I’ve mentioned before, your 75-gallon TruVu Aquasystem has a built-in wet/dry trickle filter that provides terrific biological filtration. With a tank like that you only need a very shallow gravel bed or substrate. If you don’t want to use any live sand, then I would suggest using a good calcareous aquarium gravel such as dolomite, aragonite, or crushed oyster shell about 1 inch deep, since the buffering ability of such substrates will help maintain the proper pH. (But I would avoid crushed coral or coral sand because the eventually tends to harden into a concrete-like agglomerate as it gradually dissolves.)

Don’t use a gravel bed much deeper than about an inch or so in the main tank, since a deeper gravel bed will detract from the height of the water column and might lead to anaerobic pockets where hydrogen sulfide could accumulate. Just ask a good local fish store in your area to recommend a good brand of dolomite or aragonite substrate designed for use in a marine aquarium, and tell them you need enough of it for a gravel bed no more than one-inch deep for a 75-gallon aquarium.

Since you are adamant about not having any live rock or live sand in your seahorse tank, which is just fine if that’s what you prefer, you might consider using some pest-free, dried foundation rock in the aquarium instead. Over time, it will become "alive" and house good populations of beneficial nitrifying and denitrifying bacteria within its porous structure, so it can therefore eventually provide many of the same benefits as live rock with absolutely no danger of introducing any aquarium hitchhikers or unwanted pests along with the rock, as discussed below:

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Pest-Free Dry Rock

Another good option, which is the safest and easiest procedure for most home hobbyists (especially those new to the hobby), is to start out with "dead" foundation rock instead of live rock. This dead or dry foundation rock is considerably cheaper than live rock and is, of course, completely free of undesirable pests and unwanted hitchhikers. But it will quickly enough becomes alive once it’s placed in the aquarium as it’s overgrown by algae and inhabited by copepods, amphipods and myriad microfauna. And over time the porous dead/foundation rock will become inhabited by a thriving population of nitrifying bacteria, giving it biofiltration ability. Eventually the oxygen-deprived interior of the "dead" rock will be populated by aerobic denitrifying bacteria, which convert nitrate to nitrogen gas, thereby helping to keep the nitrate levels in the aquarium under control.

By this point, the foundation rock will be very much alive and can provide all the benefits of live rock with none of the risks. The inert foundation rock looks completely natural when surrounded by living, growing macroalgae, especially when it becomes encrusted by microalgae or coralline algae, as the case may be.

The drawback to this approach is that it takes considerably longer for a new marine aquarium to cycle from scratch using dry rock than it does with live rock, and you must "seed" the tank with beneficial nitrifying bacteria from another clean source in order to start the cycling process. But the advantage of using dead foundation rock is the cheaper cost and, above all, the fact that it completely eliminates unwanted hitchhikers such as Aiptasia rock anemones, bristleworms, mantis shrimp, hydroids, and rock crabs. If they are patient, many home hobbyists feel the advantages outweigh the drawbacks.

One good source for such dry foundation rock is Macro Rocks, which offers dead, dried ocean rock in a number of interesting formations and a wide variety of types (Florida, Fiji, Tonga, etc.). They offer many beautiful, unique and intricate formations of dried ocean rock that would be an asset to any seahorse setup. Best of all, you can even purchase the Macro Rocks precycled and carrying a full complement of beneficial nitrifying bacteria, which allows you to cycle a new aquarium using the Macro Rocks as fast as an aquarium with live rock.

Macro Rocks are available online at the following website:

http://www.marcorocks.com/index.asp?PageAction=VIEWCATS&Category=14
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Best of luck finding the perfect substrate for your tastes when you are preparing your 75-gallon TruVu Aquasystem, hobby.

Respectfully,
Pete Giwojna