Why Choose a 20 Gallon Fish Tank?

A 20-gallon fish tank is often recommended as the ideal starter tank for people new to the aquarium hobby. But what makes 20 gallons a great size for beginners and experienced aquarists? This comprehensive guide covers everything you need to know about setting up, stocking, and maintaining a thriving 20-gallon freshwater aquarium.

The Benefits of a 20 Gallon Fish Tank

Compared to smaller nano tanks, a 20 gallon aquarium gives you much more flexibility and room for error regarding water parameters and fish care. The additional water volume is more stable and forgiving of small mistakes. A 20 gallon tank also allows for more aquascaping creativity and options for fish.

Some key advantages of a 20 gallon fish tank include:

  • More stable water parameters compared to smaller tanks
  • Additional filtration capacity for cleaner water
  • Space for a community of small schooling fish
  • Allows aquascapes with rockwork, driftwood, and plants
  • Room for bottom dwellers like corydoras catfish
  • Easy access for aquarium maintenance and feeding
  • Fits well in most homes without taking up too much space

For first-time fishkeepers, a 20-gallon aquarium is a great compromise between very small desktop tanks and large showpiece setups. The moderate size makes it easier to learn the ropes of testing water, doing partial water changes, and getting into a routine of aquarium care.

20 Gallon Tank Dimensions

There are two main configurations for a 20 gallon fish tank – the 20 gallon “long” and the 20 gallon “high.”

20 Gallon Long

A 20 gallon long aquarium has dimensions of 30 x 12 x 12 inches. The wider 30 inch length allows for more horizontal swimming space for active fish than taller tanks. The 12-inch height is easy to reach into for aquascaping and maintenance.

The long footprint also leaves room for larger rock formations and driftwood hardscapes. The wider surface area improves gas exchange, which benefits fish respiration.

20 Gallon High

The 20 gallon high has dimensions of 24 x 12 x 16 inches. The increased height opens up options for tall plants like Vallisneria and allows a deeper substrate bed. Fish like cichlids and bettas that inhabit all water levels appreciate the taller tank.

The smaller 24 inch length does limit horizontal swimming space compared to the long format. But the high tank style can fit in more compact spaces while offering 20 gallons of water.

Types of 20 Gallon Aquariums

There are a few options for selecting an actual 20 gallon fish tank. Tanks typically come in Glass or acrylic; you’ll also need to get a tank only or a full aquarium kit.

Glass vs. Acrylic

The most classic aquarium material is Glass. Glass tanks are economical, transparent for optimal viewing, and have high clarity. The main downside is that a 20 gallon glass tank can easily weigh over 200 pounds when filled with water and decor.

Acrylic tanks are much lighter than Glass. They also have high transparency and are very durable. Acrylic withstands hard knocks better than Glass. However, acrylic tanks typically have a higher price tag. Over time they can also show fine scratches on the surface.

For a 20 gallon freshwater setup, either glass or acrylic tanks will suit most needs. Glass is more common for smaller tanks, while large acrylic tanks are prized for their strength and weight savings.

Tank Only or Full Aquarium Kit?

Purchasing an aquarium tank by itself allows you to hand-pick all the separate components like the filter, heater, and hood. This gives you total control over the setup. But it does require researching compatible parts and equipment.

For simpler setup, a 20 gallon tank kit bundles all the essentials in one package. A basic kit includes the tank, hood or light, filtration system, and sometimes extras like a heater. While kit options are more limited, everything is guaranteed compatible and ready for quick setup.

Tank kits often provide a cost saving compared to buying individual parts a la carte. But you have less customization over brands and models. Tank-only bundles offer the most flexibility for an ideal system.

Setting Up Your 20 Gallon Aquarium

Once you’ve selected the ideal 20 gallon tank option, it’s time to set it up with substrate, equipment, decor, and water. Here is an overview of installing and cycling a new 20 gallon freshwater tank:

Equipment Needed

  • Tank stand – Sturdy stand or furniture rated for 200+ lbs
  • Filter – Hang-on-back or canister filter rated for 20-30 gallons
  • Heater – Preset to 78°F for tropical fish
  • Thermometer
  • Lighting – Fluorescent or LED aquarium light
  • Air pump & accessories (optional) – For supplemental aeration

Step-by-Step Setup

  • Rinse the tank, decorations, and gravel thoroughly before use.
  • Install background if using – Styrofoam sheets or plastic wallpaper.
  • Add 1-2 inches of gravel substrate suited for freshwater. Slope substrate if creating landscaped terraces.
  • Hardscape decor – Position wood, rocks, cave formations.
  • Fill tank with dechlorinated water slowly to avoid disturbing hardscape. Leave space at top for equipment.
  • Install filter, heater, and other equipment like air stone.
  • Cycle tank for 4-6 weeks fishless or with hardy fish. Test ammonia and nitrites frequently.
  • Adjust to 0 ammonia, 0 nitrites, <20 nitrates before adding fish!
  • Gradually acclimate fish to tank water in a drip method over an hour. Start with hardy species.
  • Enjoy your thriving 20 gallon aquarium! Maintain with partial water changes and filter cleaning.

How Many Fish for a 20-gallon Tank?

A common rule for stocking freshwater tanks is 1 inch of adult fish length per gallon of water. A 20-gallon tank would thus support about 20 inches of total fish. This guideline doesn’t factor in all aspects of bioload, activity levels, and species compatibility. But it provides a reasonable starting estimate for stocking.

Based on the 1 inch of fish per gallon rule, here are some general 20-gallon tank stocking ideas:

  • 10 neon tetras (1.5 inches each)
  • 1 pearl gourami (3 inches) + 6 harlequin rasboras (1.5 inches)
  • 8 zebra danios (1.5 inches) + 6 pygmy cories (1 inch)
  • 1 dwarf gourami (2 inches) + 6 black skirt tetras (2 inches)
  • 2 honey gourami (2.5 inches) + 8 ember tetras (1 inch)
  • 1 betta (2.5 inches) + 7 habrosus cories (1 inch) + 6 chili rasboras (1 inch)

These are just a few possible combinations for a moderately stocked 20 gallon community tank. Monitor water parameters closely as fish grow and adjust stocking or increase maintenance accordingly.

Best Fish for a 20 Gallon Aquarium

With the appropriate selection of fish, a 20-gallon freshwater aquarium can support a vibrant community tank. Here are some top choices:


Tetra fish are classic community species perfect for 20 gallon tanks. Neon tetras, black skirt tetras, ember tetras, and rummynose tetras are bright, active schooling fish under 2 inches long. Keep groups of 6-10 fish.


Rasbora species like harlequin rasboras stay small, seldom exceeding 2 inches long. They are peaceful schoolers who bring movement and color to the midwater zone. Keep groups of 6 or more.


Gouramis like honey and pearl gouramis, have an L-shaped labyrinth organ that allows them to breathe air. A 20 gallon tank has room for 1-2 medium-sized gourami and other fish. Avoid mixing aggressive gourami species.

Corydoras Catfish

Bottom-dwelling cory cats help clean debris and are entertaining to watch. Pygmy corydoras and habrosus corydoras only grow to about 1 inch, making them ideal for smaller tanks. Keep corydoras in schools of 6+ fish.


Small pleco species like clown plecos or bristlenose plecos can be incorporated into a 20 gallon community tank. Avoid common plecos, which can reach up to 2 feet long! Choose plecos under 5 inches in length.

Best Plants for a 20 Gallon Aquarium

Live aquarium plants help absorb fish waste, provide oxygen, and give fish places to explore and hide. Some great plant choices for a 20 gallon freshwater tank include:

Background Plants:

  • Vallisneria

Midground Plants:

  • Amazon Sword
  • Cryptocorynes
  • Java Fern

Foreground Plants:

  • Dwarf Sagittaria
  • Dwarf Hairgrass
  • Pygmy Chain Sword

Floating Plants:

  • Hornwort
  • Anacharis
  • Frogbit


  • Java Moss
  • Christmas Moss
  • Flame Moss

Carpet Plants:

  • Monte Carlo
  • Glossostigma
  • Pearlweed

Aim for fast-growing stem plants to absorb excess nutrients and help stabilize the aquarium. Easy plants like anacharis, hornwort, and vallisneria are great for beginner-friendly tanks. Plant heavily from the start or algae may become an issue before the plants fill in. Research plant care requirements, lighting needs, and growth rates when selecting. Aquatic plant fertilization and liquid CO2 can accelerate growth if needed.

Here are a few sample 20 gallon aquarium aquascapes:

  • Tall background plants like Vallisneria, midground swords and crypts, and a Java moss foreground.
  • Driftwood centerpiece surrounded by Java fern and anacharis stems. Carpet the foreground with dwarf sagittaria.
  • Hardscape one side with rocks supporting epiphyte plants like anubias and bucephalandra. Plant hairgrass on the opposite side.
  • Aquascaping a planted tank takes planning but adds beauty and natural appeal. Consider arranging plants and hardscape to create your ideal 20 gallon layout.

20 Gallon Aquarium Maintenance

Caring for your 20 gallon tank involves regular maintenance to support fish health. Key tasks include:

Water Changes

20-30% weekly water changes are recommended for lightly stocked community tanks. Replace water lost to evaporation between changes. Use a gravel vacuum to remove debris.

Filter Maintenance

Clean mechanical and biological filter media monthly to maintain good water flow and remove waste. Rinse sponges in old tank water only.

Equipment Checks

Verify equipment like heaters, air pumps, and lights are working properly. Replace worn parts as needed.

Algae Control

Control lighting duration to 6-8 hours daily. Remove visible algae, supplement Excel or CO2. Introduce algae eaters like otocinclus catfish.

Testing Water

Test for ammonia, nitrite, nitrate 1-2 times monthly or when problems occur. Ideal levels are 0 ammonia/nitrites, <20 nitrates.


Trim plants as needed, replant stems, rearrange decor for ideal growth and aesthetics.

20 Gallon Aquarium Tank Mates

Compatible tank mates are key to a peaceful community aquarium. Avoid mixing slow and fast fish, aggressive species, or fish with vastly different care needs. Some great 20 gallon tank mates to consider include:

  • Tetras, rasboras, or danios
  • Gouramis, bettas, or dwarf cichlids
  • Corydoras, otocinclus, or bristlenose plecos
  • Shrimp like cherry, ghost, or amano shrimp
  • Snails such as nerites, mysteries, or ramshorns

Research species before selecting tank mates. Slower moving fish like bettas may be fin-nipped by fast tetras. Large cichlids can’t be mixed with small shrimp or tetras.

Mix species with similar water parameter needs. Most community fish thrive in the same neutral pH and moderate hardness conditions. Select peaceful schooling fish that occupy different tank areas.

20 Gallon Aquarium Fish Tank Stand

A sturdy aquarium stand is a must-have for any tank 20 gallons or larger. Water weighs over 8 pounds per gallon – a 20 gallon tank will weigh nearly 250 lbs filled! Purchase a stand specifically designed for fish tanks rather than general furniture.

Consider these factors when selecting a 20 gallon aquarium stand:

  • Strength rating of at least 250 lbs
  • Material such as wood or metal
  • Width and depth fit the tank’s footprint
  • Styling matches your decor – open or enclosed
  • Provides storage space for supplies

A quality tank stand provides level support at the proper height for viewing. Some stands include removable panels or doors to access equipment easily. To build your custom stand, use dense lumber-like oak reinforced with triangulation for maximum strength.

Many 20 gallon tank kits include a matching stand with the aquarium. While convenient, these stands sometimes cut corners on materials and aren’t as durable. Weigh your options – a good stand protects your investment in the tank.

How Much Does a 20 Gallon Fish Tank Cost?

A new 20 gallon aquarium setup can cost $200-500, depending on the quality of equipment chosen. Here is an overview of estimated costs:

  • Fish Tank – $50-150 for Glass or acrylic 20 gallon tank
  • Filter – $40-100 for hang-on-back or canister filter rated for 20-30 gallon tanks
  • Heater – $20-60 for 50-100 watt submersible aquarium heater
  • Light – $40-80 for LED or fluorescent hood or clip-on light
  • Substrate – $20-40 for a 20 lb bag of gravel or aquasoil
  • Decor – $20-60 for rocks, driftwood, artificial decor
  • Plants – $10-40 depending on live plants selected
  • Stand – $60-200 for tank-specific stand
  • Additional equipment like air pumps or timers

Depending on type, fish and tank mate species will cost $5-20 per fish. Buying a complete 20 gallon kit can save some costs but limits customization. Prioritize essentials like filtration and slowly accumulate other gear.

Where to Buy a 20 Gallon Aquarium

20 gallon fish tanks are readily available at most major pet stores. Here are some options, both online and local:

  • Petco
  • Petsmart
  • Pet Supplies Plus
  • Walmart
  • Amazon
  • Local fish stores
  • Aquarium co-ops
  • Direct from brands like Aqueon

Shop around for sales and price comparisons between retailers: review warranties, return policies, and shipping costs for online purchasing. Consider buying used tanks from resellers like Craigslist for savings. Seek out high-clarity glass or optically pure acrylic tanks for the best visibility. Low iron glass has enhanced transparency and lacks green tinting. Kits may include lower-grade Glass or acrylic. Inspect tanks thoroughly before purchase – avoid chips, major scratches, or silicone damage. A 20 gallon tank can last years with proper care and equipment maintenance.

Frequently Asked Questions

Here are answers to some common questions about setting up and maintaining a 20 gallon freshwater aquarium:

What size stand should I get for a 20 gallon tank?

Look for a stand 24-30 inches long by 12-18 inches deep to match the footprint of a 20 gallon tank. Double check exact tank dimensions before purchasing.

How often should water changes be done on a 20 gallon aquarium?

Aim for 20-25% partial water changes weekly for a lightly stocked community 20 gallon tank. Test water parameters regularly and increase frequency if nitrates exceed 20 ppm.

What kind of filter is best for a 20g tank?

A hang-on-back or canister filter rated for 20-30 gallon tanks will work well. Look for models with adjustable flow rates around 100-150 GPH.

How many fish can I put in a 20-gallon tank?

Generally, you can house 1 inch of adult fish length per gallon of water. So for a 20 gallon tank, shoot for no more than 15-20 inches of fish. This depends on species and filtration capacity.

Is a 20 gallon tank easy to maintain?

A 20 gallon aquarium is one of the most manageable sizes for beginners. Larger tanks can be more difficult, while smaller tanks have less stable water parameters. 20 gallons strikes a nice balance.

Final Thoughts

A 20-gallon freshwater tank is perfect for new and experienced aquarists. Compared to pint-sized nano tanks, 20 gallons gives you far more options while remaining inexpensive and easy to care for. You’ll enjoy the flexibility to create planted layouts, pick compatible tank mates, and establish a thriving aquatic community.

With a quality 20-gallon tank, filtration, heating, lighting, and decor – you’re well on your way to an enjoyable, low-maintenance underwater world. A 20-gallon aquarium allows creativity and forgiveness as you learn the ins and outs of the hobby. Why not give it a try? You might get hooked!