Best 20-Gallon Fish Tank: 20 Long or 29?
3 minute read · Updated November 10, 2026
Edited by Ivan F.
Quick answer
For most community fish, a 20-gallon long is the easier shape, because it gives more floor and surface than a 20 high. A 29 has the same footprint with more height, which suits taller fish. Plan for about 225 to 330 lb filled, and a stand built for it.
Why this size is easier
A veterinary hospital says most people start with a 10- or 20-gallon tank, and a welfare charity says larger volumes hold more stable temperatures and water conditions. A 20 to 29-gallon tank gives you room for a small community without the weight of a large tank.
In liters, by our arithmetic, a 20-gallon tank holds about 76 liters and a 29 about 110.
Three common shapes
| 20 high | 20 long | 29 | |
|---|---|---|---|
| Length × width | About 24 × 12.5 inches | About 30 × 12.5 inches | About 30 × 12.5 inches |
| Height | About 17 inches | About 13 inches | About 19 inches |
| Filled weight | 225 lb | 225 lb | 330 lb |
| Suits | Small spaces, taller decor | Schooling fish and bottom dwellers | Taller fish, or more water on the same stand |
Sizes and weights are from one maker’s chart, rounded, and other makers may differ by a little. Which shape suits which fish is our advice.
How to choose
- Surface first. A welfare charity says wide tanks are better than tall ones, because surface area is where oxygen enters. A veterinary manual bases one stocking guide on surface: 1 inch of fish for every 12 square inches.
- Length for swimmers. One retailer suggests a 20-gallon long for fish that need swimming length.
- Height for tall fish. The same retailer says tall-bodied fish, such as angelfish, need vertical height. A 29 gives that on the same footprint as a 20 long.
- A stand built for it. A veterinary manual says the floor and stand must be strong, level and stable, and the maker says a suitably designed stand is essential.
Bare tank or kit?
A kit bundles the tank with a hood, a light and usually a filter. Some also include a heater, and some of those are preset to one temperature. A bare tank lets you choose each part. Either way, check that the filter and heater suit your fish, and add a lid if the tank has none.
Before you fill it
- Place it out of direct sunlight, which a veterinary manual says to avoid.
- Check the floor. A filled 29 is heavy, so put it near a wall on a solid floor.
- Plan the rest. Budget for a water conditioner, a test kit, a thermometer and substrate, then cycle the tank before adding fish.
Browse fish that suit a 20-gallon tank to plan a community.
Options that fit
Chosen against the criteria above. Nobody at AquariaWiki has used or tested these products. The specifications are the makers' own statements, so these are the strongest fits on the facts we could record, not a hands-on verdict.
Picks for the US
Aqueon Standard Glass Aquarium 20 Long US
The shape this page suggests for most community fish: long and shallow, with plenty of floor and surface. It is a bare tank, so add a lid, a filter and a heater, and check that your stand is made for the filled weight.
The manufacturer states: Size 20 Long. 30.25 x 12.5 x 12.75 inches. 225 lb filled by the maker's size chart, which says filled weights vary with substrate and decor. Place it on a stand able to bear the filled weight. 5-year warranty.
Aqueon Standard Glass Aquarium 29 Gallon US
The same footprint as the long tank above with more height, for taller fish such as angelfish, or more water on the same stand. It is heavier, so check the stand's rating. It is a bare tank, so add a lid, a filter and a heater.
The manufacturer states: Size 29. 30.25 x 12.5 x 18.75 inches. 330 lb filled by the maker's size chart, which says filled weights vary with substrate and decor. Place it on a stand able to bear the filled weight. 5-year warranty.
Picks for Spain
Eheim clearTank 73 Spain
The only tank at this size we could confirm for Spain. It holds a little less than the US tanks above, so check each animal's minimum before you stock it. It is a bare tank of optical glass, so add a lid, a filter and a heater.
The manufacturer states: 73 liters. 60 cm wide, 35 cm deep and 35 cm tall. 5 mm optical glass. 3-year warranty.
Frequently asked questions
Is a 20 long or a 20 high better?
For most beginners, the 20 long. A welfare charity says wide tanks are better than tall ones, because surface area is where oxygen enters. A 20 high suits tall decor or taller fish, and takes less floor space.
What is the difference between a 20 long and a 29?
In one maker's chart, they share the same footprint, about 30 by 12.5 inches. The 29 is about 6 inches taller and holds more water, so it weighs more and gives taller fish room.
How heavy is a 29-gallon tank?
One maker's chart lists its 29-gallon at 330 lb filled, and its 20 long at 225. Filled weight depends on substrate and decor, so allow some margin.
Does a 20-gallon kit include a heater?
Some do, some do not, and some include a preset heater that holds one temperature. Read the box against your species' range before you buy.