Keeping an aquarium can be a rewarding hobby, but determining how many fish can happily live in your tank is key. This complete guide will provide you with everything you need to know about stocking a 20 gallon freshwater aquarium.
What are the Key Factors That Determine Capacity
There are a few main considerations when figuring out how many fish a 20 gallon tank can support:
Tank Dimensions
A standard 20 gallon aquarium has base dimensions of 24” x 12” and is about 16” tall. The footprint and volume impact how much swimming space is available.
Filtration System
You need an external canister filter or internal power filter that provides enough filtration capacity for the bioload of your chosen fish.
Fish Size and Behavior
Bigger fish need more room, while territorial fish need their own space. Small schooling fish can be stocked more densely.
Aquascaping and Decorations
The layout of plants, rocks, driftwood and other decor takes up space that fish can’t use. A heavily decorated tank supports fewer fish.
With those factors in mind, let’s look at how many fish are recommended for a 20 gallon aquarium.
What is the Recommended Number of Fish for a 20 Gallon Tank
Most experts recommend stocking 1 inch of adult fish per 1-2 gallons of water, depending on filtration capacity and fish size.
For a 20 gallon tank, this equals:
- 20-40 small fish like neon tetras or guppies
- 10-15 medium fish like mollies or platies
- 5-10 larger fish like angelfish or gouramis
To maximize fish health, it’s best to aim for the lower end of those ranges.
Here are some examples of fish combinations that work well in a 20 gallon aquarium:
| Tank Size | Fish Combination |
|---|---|
| 20 gal | 10 neon tetras, 6 corydoras catfish |
| 20 gal | 1 angelfish, 6 harlequin rasboras, 6 kuhli loaches |
| 20 gal | 1 dwarf gourami, 6 cherry barbs, 5 zebra danios |
Mix small, medium and bottom-dwelling fish for best results. Avoid aggressive fish like tiger barbs in a small tank.
Now let’s go over the tank size requirements for some popular freshwater fish species.
Fish Species and Recommended Tank Sizes
To prevent stunting and stress, it’s important to follow recommended tank sizes for each fish species. Here are the minimums for popular freshwater fish:
Small Fish
| Fish | Minimum Tank Size |
|---|---|
| Neon Tetra | 10 gallons |
| Guppies | 10 gallons |
| Endler’s Livebearer | 10 gallons |
| Zebra Danio | 10 gallons |
| White Cloud Mountain Minnow | 10 gallons |
| Cherry Barb | 20 gallons |
Small schooling fish like tetras, rasboras, danios and minnows need at least 10 gallons for a group, while slightly bigger fish like cherry barbs do better in 20 gallon long tanks.
Medium Fish
| Fish | Minimum Tank Size |
|---|---|
| Mollies | 20 gallons |
| Platies | 20 gallons |
| Swordtails | 20 gallons |
| Gouramis | 20 gallons |
| Rainbowfish | 30 gallons |
Most medium-sized community fish require at minimum a 20 gallon tank, while rainbowfish need more swimming room and do best in 30+ gallon aquariums.
Large Fish
| Fish | Minimum Tank Size |
|---|---|
| Angelfish | 29 gallons |
| Discus | 55 gallons |
| Oscar | 55 gallons |
| Silver Dollar | 55 gallons |
| Jack Dempsey | 55 gallons |
Large cichlids need bigger tanks – angelfish need at least 29 gallons for a pair, while oscars, jack dempseys and other big cichlids require 55+ gallon tanks. Avoid cramming them into small aquariums.
Overstocking Dangers: Issues Caused by Too Many Fish
It can be tempting to purchase more fish than your aquarium can support, but overstocking a tank causes numerous problems including:
- Poor water quality: Excess waste, ammonia and nitrates stress fish and cause disease. Overwhelmed filters can’t keep up.
- Aggression and territorial issues: Some fish get aggressive when cramped, while others need personal space.
- Stunting: Fish can’t grow to full size and become deformed and sickly.
- Shorter lifespans: The stresses of overcrowding lead to premature death.
- Oxygen depletion: Too many fish can literally suck the oxygen out of the water.
Avoid overstocking by sticking to the one inch of fish per gallon rule. Only get species suited to your tank size, and resist impulse purchases. Perform regular partial water changes and filter maintenance to remove waste and replenish oxygen.
Aquarium Stocking Tips and Tricks
Here are some tips for safely stocking your 20 gallon tank while providing a healthy, thriving environment:
- Add fish slowly – Start with just a few hardy fish and build up gradually over several weeks. This allows bacteria colonies to grow to handle the increasing bioload.
- Research species needs – Check water parameters, adult sizes, behavior, tankmates and diet before acquiring any fish.
- Include bottom dwellers – Add cleanup crew fish like cory catfish, loaches and plecos which help eat waste.
- Mix active and passive fish – Balance schooling fish with less active ones to prevent aggression.
- Pay attention to tank height – Tall bodied fish like angels and gouramis need height, while long-finned fish prefer length.
- Leave open swimming space – Even small fish need room to dart around. Arrange decorations thoughtfully.
- Quarantine new arrivals – Isolate and observe new fish in a separate tank for a few weeks before adding to your display.
- Test water frequently – Check ammonia, nitrite, nitrate and pH levels weekly and before adding more fish.
Following these best practices will lead to a healthy, long-lasting aquarium with happy fish.
Conclusion
Determining how many fish can comfortably live in a 20 gallon freshwater aquarium depends on the species, adult sizes, behaviors, tank dimensions and filtration capacity. Aim to provide at least 1 inch of adult fish length per 1-2 gallons of water.
Ideally, stock a 20 gallon tank with small schooling fish like tetras, a few medium-sized fish like platies, and bottom feeders like corydoras. Avoid aggressive fish and those requiring larger tanks. Build your population gradually, quarantine new additions, and test water quality frequently.
Follow the one inch per gallon rule, research your fish, and leave ample open swimming space. With careful stocking, filtration, and tank maintenance, your 20 gallon aquarium can be a thriving underwater community.
Frequently Asked Questions
Can I put a betta fish in a 20 gallon tank
Yes, you can keep a single male betta or a female sorority in a 20 gallon tank. The extra space allows for plenty of swimming room and decoration possibilities. Make sure any tankmates are peaceful and won’t nip fins.
What about African cichlids in a 20 gallon aquarium
African cichlids generally need larger tanks since they are aggressive and grow quickly. Even dwarf cichlid species like shell dwellers need 20 gallons per pair, so a 20 gallon tank can only support one mated pair comfortably. Avoid mixing African cichlid species.
Are plecos good for a 20 gallon aquarium
Small pleco species like clown or bristlenose plecos can work well in a 20 gallon tank. Avoid common plecos, which quickly outgrow this size. Make sure to provide driftwood for grazing. Limit to 1 pleco so they don’t overload the bioload.
Can goldfish or koi live in a 20 gallon tank
No, goldfish and koi require much larger aquariums than 20 gallons. Fancy goldfish need at least 30 gallons for the first fish and 10-20 gallons for each additional