When browsing for a new aquarium, the total volume in gallons or liters is usually the first specification listed. You might decide you want a 20-gallon tank for your bedroom and head to the pet store. However, once there, you will face a choice: Do you want a 20-gallon "High" or a 20-gallon "Long"? They both hold exactly 20 gallons of water. Does the shape really matter?
If you are planning to build a high-tech planted tank or a detailed aquascape, the shape—specifically the "footprint" and the height—matters vastly more than the total volume. The dimensions of the glass box will dictate what kind of plants you can grow, how much money you will spend on lighting, and how easily you can maintain biological balance. In this article, we will explore why the physical dimensions calculated by an Aquarium Volume Calculator are the most critical blueprint for aquascaping success.
Defining the Footprint
The "footprint" of an aquarium refers strictly to its base dimensions: the Length multiplied by the Width (front-to-back depth). It represents the total surface area of the bottom of the tank.
- A standard 20-Gallon High has a footprint of 24 inches long by 12 inches wide (288 square inches). It achieves its 20-gallon volume by being 16 inches tall.
- A standard 20-Gallon Long has a footprint of 30 inches long by 12 inches wide (360 square inches). It achieves the exact same volume by being only 12 inches tall.
Despite having identical water volumes, these two tanks offer completely different environments for aquatic plants.
The Tyranny of Tank Height (Depth)
In planted aquariums, Light and Carbon Dioxide (CO2) are the two primary fuels for photosynthesis. The taller (deeper) an aquarium is, the harder it becomes to provide these fuels to the plants at the bottom.
1. Light Penetration and PAR
Light intensity diminishes rapidly as it travels through water. Aquarists measure usable light for plants in a metric called PAR (Photosynthetically Active Radiation).
- If you place a standard LED aquarium light over a shallow 12-inch tall tank, a high percentage of that PAR reaches the substrate, allowing you to grow demanding, light-hungry carpeting plants like Hemianthus callitrichoides (Cuba) or Glossostigma elatinoides.
- If you place that exact same light fixture over a 24-inch tall tank, the light scatters and weakens before it hits the bottom. To grow those same carpeting plants at that depth, you would have to spend hundreds of dollars on a highly specialized, ultra-powerful lighting system.
Tall tanks restrict you to growing low-light plants (like Anubias and Cryptocoryne) at the bottom, while requiring fast-growing stem plants to reach the surface to find light.
2. CO2 Distribution and Flow
High-tech planted tanks rely on injected CO2 gas to boost plant growth. The goal is to dissolve this gas into the water and use the filter's current to push it down into the carpet plants.
- In a shallow, long tank, water flow easily sweeps across the bottom, delivering a steady stream of CO2 to the lowest leaves.
- In a tall tank, the water flow from the filter often circulates near the top half of the water column, creating "dead spots" at the bottom where CO2 never reaches. This leads to stunted plant growth and localized algae blooms on the substrate.
The Aquascaping Advantage of a Large Footprint
Beyond the physics of light and gas, the footprint dictates the artistic potential of the tank. Aquascaping is the art of creating underwater landscapes, often utilizing principles like the "Golden Ratio" and the "Rule of Thirds."
Creating Depth and Perspective
To make an aquarium look like a vast, endless landscape, aquascapers slope the substrate, placing rocks and wood to create vanishing points.
- Narrow Tanks: If a tank is only 10 inches wide (front-to-back), you have almost zero room to slope the soil or layer plants from front to back. The resulting scape often looks flat, like a 2D painting pressed against the glass.
- Wide Tanks (Deep Footprints): A tank that is 18 to 24 inches wide front-to-back allows for massive, sweeping slopes. You can plant a foreground carpet, a dense midground of bushes, and a towering background of stem plants. This creates a mesmerizing 3D diorama effect.
Swimming Space for Schooling Fish
The footprint also dictates your livestock choices. A school of Rummy-nose Tetras needs horizontal sprinting space to display their natural, tight schooling behavior. A 30-gallon tall tank, shaped like a column, forces them to swim in frustratingly tight circles. A 30-gallon long tank gives them a runway to swim and exhibit natural behaviors, which in turn reduces their stress and improves their coloration.
Popular "Breeder" Tanks: The Aquascaper's Choice
If you look at the tanks used by professional aquascapers, you will notice a trend. They rarely use standard "High" tanks. Instead, they favor "Breeder" dimensions.
Tanks like the 40-Gallon Breeder (36"L x 18"W x 16"H) are legendary in the hobby. They offer a massive 18-inch front-to-back depth for incredible scaping layouts, while remaining only 16 inches tall, ensuring that even mid-range LED lights can push enough PAR to the substrate to grow lush carpets.
Before purchasing a tank solely based on the gallon count on the sticker, use our Aquarium Volume Calculator to play with the dimensions. Think about the physical dimensions first, and let the total volume be a secondary result.
Frequently Asked Questions (FAQ)
Can I grow a carpet in a tall aquarium?
Yes, but it is much more difficult and expensive. You will need a high-end, penetrating LED fixture (often using focused lenses), excellent flow circulation to push CO2 to the bottom, and you may need to build up the substrate height in the back to bring the plants closer to the light source.
What is the best shape for a beginner planted tank?
The standard 20-Gallon Long (30"L x 12"W x 12"H) is arguably the best beginner planted tank. It is shallow enough that cheap lights work well, long enough to allow for interesting hardscape layouts, and holds enough water to maintain stable water parameters.
Does a larger footprint increase evaporation?
Yes. Evaporation occurs at the surface where the water meets the air. A tank with a large footprint has a greater surface area exposed to the air, meaning water will evaporate faster than in a tall, narrow tank of the same volume. You will need to top off the water more frequently.
In the world of planted aquariums, the shape of the canvas is just as important as the paint you put on it. Prioritizing a large footprint and a shallow height over sheer total volume will make your journey into aquascaping vastly easier and visually rewarding.
