Having an aquarium can be a fun and relaxing hobby, even if you only have room for a small 3 gallon tank. With some planning and proper fish selection, a 3 gallon tank can make an enjoyable pet habitat.

If you’re short on time, here’s a quick answer to your question: Small, peaceful fish like bettas, guppies, tetra species, and dwarf corydoras catfish can thrive in a filtered, heated 3 gallon tank when kept singly or in very small numbers.

Choosing the Right Fish for a 3 Gallon Tank


Bettas, also known as Siamese fighting fish, are a popular choice for small tanks like 3 gallons. These colorful fish can thrive in such confined spaces because they do not require much room to swim around.

Male bettas in particular should never be housed together, as they will fight, hence their name. But a single betta makes an ideal 3 gallon tank inhabitant.

Care should be taken to not put bettas with aggressive fish who might nip their flowing fins. But peaceful community fish like neon tetras or dwarf cories can complement bettas well. Make sure any tankmates do not have brightly colored fins that your betta might mistake for those of its own species.


Guppies are another common fish for small freshwater tanks. Their diminutive size, vibrant colors, and peaceful temperaments allow them to adjust nicely to tanks as small as 3 gallons.

These livebearers will readily breed in your tank, however, so either choose only male guppies or be prepared to give away any fry. Have plenty of hiding spots among plants and ornaments where newborn guppies can shelter themselves from hungry adult guppies.

Tetra Species

Many tetra species, like neon tetras, ember tetras, and galaxy rasboras, thrive in lightly stocked 3 gallon aquariums when kept in proper schools of 6 fish or more. Their small stature allows them to navigate modest tank volumes, and their shoaling behavior is fascinating to watch.

Avoid larger tetras like black skirts in such a small enclosure. Stick to tetras that only grow to about an inch long. Providing some aquarium salt can help prevent common maladies in tetras like neon tetra disease.

Dwarf Corydoras Catfish

The pygmy cory and hastatus cory species are catfish that seldom surpass an inch in length. This makes them great scavengers for picking up leftover fish food in a 3 gallon community tank. Keep them in groups of 6 or more, giving them plenty of hiding spots among tank decor.

Their barbels and armored bodies should be protected from sharp objects in the tank. Smooth gravel substrate is best, and make sure decor has no rough edges. Feed them occasional treats like brine shrimp along with standard cory foods to keep them well nourished.

Setting Up the 3 Gallon Aquarium Environment


Proper filtration is crucial for maintaining water quality in a 3 gallon aquarium. A hang-on-back power filter or small canister filter with a low flow rate would work well. Aim for a filter rated for 5-10 gallons, as you want one with enough capacity to handle the bioload.

Add filtration media like foam, ceramic rings, and activated carbon to remove debris, provide surface area for beneficial bacteria, and absorb dissolved organic compounds. Perform regular maintenance by rinsing the mechanical media in old tank water at water changes and replacing chemical media per manufacturer instructions to keep the filter running efficiently.


Most fish species require tropical water temperatures around 75-82°F. A mini submersible heater with built-in thermostat (25-50 watts) can safely and accurately heat the small volume of water. Place the heater horizontally near the filter outlet to promote water circulation.

Monitor the temperature daily and make adjustments as needed to maintain a stable environment.

Plants and Decor

While limited on space, you can still add simple decor to enrich the tank. Small pieces of driftwood, rocks, and artificial plants help break up sight lines and create a natural habitat. Live plants like anubias, java fern, and moss can assist with filtration but require proper lighting.

Beware overcrowding the tank, as fish need adequate swimming areas. Stick to a couple of small decorations and allow open areas. Perform regular water changes and siphon the substrate to remove debris like fallen leaves.

Tank Maintenance for 3 Gallon Tanks

Water Changes

Performing regular water changes is crucial for keeping fish healthy in a 3 gallon tank. Small tanks like these are prone to dangerous ammonia and nitrite spikes, so frequent water changes are needed to dilute these toxic compounds.

A general guideline is to change out 25-50% of the water 1-2 times per week. When changing water, use a gravel vacuum to remove debris from the substrate. Replace the removed water with dechlorinated water that is the same temperature as the tank water. This will prevent shocking the fish.

Test the water regularly with a liquid test kit to monitor ammonia, nitrites, and nitrates to ensure levels stay in the safe range between water changes.

Gravel Cleaning

In addition to siphoning the gravel when doing water changes, the substrate in a 3 gallon tank should be thoroughly cleaned 1-2 times per month. This removes accumulated organic waste that can decompose and pollute the water.

To clean the gravel, remove all decorations and fish, leaving just the gravel and water in the tank. Use a gravel vacuum or siphon to disturb the top layer and draw out the dirty water. Replace with clean dechlorinated water, adding conditioners as needed to remove chlorine and heavy metals.

Thorough gravel cleaning removes nitrate buildup and provides a clean healthy environment for fish.

Filter Maintenance

The filter is the heart of a 3 gallon aquarium, so keeping it maintained is vital. Most small tanks use either a hang-on-back style or internal/submersible filter. These should be inspected monthly and cleaned as needed to remove clogged debris.

Follow manufacturer recommendations on filter media replacement. If the filter flow seems weak between cleanings, check the impeller and shafts for buildup or wear. Keep extra filter cartridges on hand so they can be swapped out during cleaning.

Avoid rinsing media in untreated tap water as this kills beneficial bacteria. Only use tank water, conditioned water or a filter revival solution. With regular maintenance, an efficient filter will keep water clean between changes.


While a bit limited in which fish can thrive, a filtered and heated 3 gallon aquarium can make for a fun desktop tank. Choosing suitable fish like bettas and small tetra or catfish species, and keeping up with critical tank maintenance can lead to success.

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