The Long and Short of Marine Aquarium Tank Shape

Here at Saltwater Smarts, we often make the case that size matters when it comes to saltwater tanks. The bigger the tank, the better for a variety of reasons (though we can’t dispute that nano tanks offer certain advantages too). However, an aquarium’s overall volume isn’t the only factor to consider. The shape of the tank is important, as well.

Why does tank shape matter? After all, a gallon of water is a gallon of water regardless of the shape of the vessel you choose to hold it in, right? Well, from the standpoint of diluting dissolved pollutants, this is true enough, but tank shape influences many other aspects of marine aquarium husbandry.

So what’s the shape of marine aquarium success? Generally speaking, shorter, wider aquariums are preferable to taller, narrower ones—even if they hold the exact same volume of water. Here’s why:

Better gas exchange

One of the most significant advantages of shorter, wider tanks over taller, narrower ones is that they offer much greater surface area. In other words, the interface between the air and water is much more substantial, allowing for optimal gas exchange. That means more efficient oxygenation of the water and off-gassing of carbon dioxide.

More swimming space

When it’s stated that a fish needs lots of open swimming space, that usually means in the horizontal plane. For most species, vertical space (beyond a reasonable depth, of course) is of little consequence. Wider tanks also make it much easier for larger fish species to turn around at either end of a rectangular aquarium.

More territories for fish/niches for corals

Tanks with a wider footprint offer more options for creative aquascaping—hence more territories for fish to claim and more niches for coral placement—because they tend to be deeper front to back. This characteristic also makes it a little easier for fish to stay out of each other’s line of sight, which can reduce the likelihood of bullying or territorial squabbling.

Better light penetration

Shorter tanks are also preferable for light-hungry corals and other photosynthetic invertebrates (e.g., tridacnid clams and anemones) because they offer superior light penetration. As a result, and depending on the species kept, you may be able to satisfy your inverts’ lighting needs with lower-wattage (and less costly) lamps.

Easier maintenance

Because you can easily reach all the way to the bottom without having to don a wetsuit, shallower tanks are generally easier to maintain than taller ones. This may seem insignificant in the grand scheme of things, but remember: the easier tank-maintenance chores are, the more likely you are to tackle them on a regular basis.

Are tall tanks out of the question?
Does all this mean that taller, narrower tanks are doomed to fail? Not at all! You can certainly succeed with one as long as you’re aware of their limitations and implement measures to compensate for them—for example, stocking lightly, increasing turbulent water movement at the surface and circulation throughout the water column to maximize oxygenation, and placing light-hungry invertebrates closer to the water surface versus closer to the bottom where light penetration is minimal.