The best 20 gallon fish tank for most people is a standard 20 long — 30 × 12 × 12 inches — bought bare, with a filter of at least 150 gallons an hour and an adjustable heater added separately. A starter kit, a rimless tank, a 20 high or an all-in-one can each be the better buy for a particular setup, so this page picks by type rather than naming one winner.
This is a short list of five tank types, numbered and kept in the same order, each with the one thing it's best for and an honest drawback. None of the slots is sponsored.
How to read this page
The picks are product types, not tanks I've tested side by side. Where I name a model, it's an example a cited reviewer recommends or a seller's own listing, not a claim from my own tanks. Prices change often, so check the retailer's page.
The short answer
Match the tank to the fish and the plants you want:
- Most community or planted tanks: a 20 long, bought bare, with your own filter and heater — pick 1.
- One box, smallest outlay, first tank: a 20-gallon starter kit — pick 2. Expect to upgrade the heater and probably the filter.
- A planted aquascape you'll look at every day: a rimless low-iron glass tank of about 20 gallons — pick 3.
- Tall fish, or not much floor space: a 20 high — pick 4.
- Equipment out of sight: an all-in-one tank with built-in filtration — pick 5.
UK tanks are usually sold in litres. A US 20-gallon tank holds about 76 litres, so in the UK look at tanks of roughly 75–80 litres with a similar footprint.
The picks
Quick comparison
| # | Tank type | Best for | Typical size (L × W × H) | Comes with | Relative cost |
|---|---|---|---|---|---|
| 1 | 20 long, bare | Most community and planted tanks | 30 × 12 × 12 in (76 × 30 × 30 cm) | Tank only | Low |
| 2 | 20-gallon starter kit | First tank, one box | Varies by kit | Hood, light, filter, often a heater | Low |
| 3 | Rimless low-iron tank | Planted aquascapes | e.g. 60 × 36 × 36 cm (about 20.5 gal) | Tank, sometimes a levelling mat | Mid |
| 4 | 20 high, bare | Tall fish, small footprint | 24 × 12 × 16 in (61 × 30 × 41 cm) | Tank only | Low |
| 5 | All-in-one with built-in filtration | Hidden equipment | Often a cube | Built-in filter section | High |
Sizes are the common standards from Top Shelf Aquatics' size chart and, for pick 3, the UNS 60U as listed by Buce Plant. "Relative cost" is a rough ranking, not a price.
How I chose
Four things decide whether a 20-gallon tank is the right one:
The footprint suits your fish. Aquarium Store Depot says the 20 long wins for almost every fish because of its swimming length, and the 20 high suits tall species. Both hold the same water; the long gives fish more room to swim and gives plants a shallower tank to light.
The equipment is good enough — or you're buying it separately. Aquarium Store Depot recommends a filter of at least 150 gallons an hour on a 20-gallon tank, and says generic kits often ship with 80–100. It also warns that preset heaters can run 2–4°F hot and recommends an adjustable one.
You have a stand that can carry it. Top Shelf Aquatics puts a filled 20 high or 20 long at about 225 lb. A rimless tank also needs a surface that supports its whole base; Aquarium Store Depot warns that discount cabinets with large gaps won't do.
It suits plants if you want them. Clear glass, no frame and room for a proper light matter more to a planted tank than to a fish-only one. Aquarium Store Depot rates UNS rimless tanks for planted setups and says budget LED strips rarely grow much beyond java moss.
Free tool
A '20-gallon' tank holds less once substrate, rock and wood go in. Work out your real water volume before you size the filter and heater.
Aquarium volume calculator →Each pick, honestly
1. 20 long, bought bare — best overall. A plain 30 × 12 × 12 inch glass tank is cheap, easy to find and gives fish the most swimming length for 20 gallons. Buying it bare means you choose the filter, heater and light yourself. Aquarium Store Depot's own build is a bare tank with a 200-gallon-an-hour hang-on-back filter and an adjustable heater, and it lists the Aqueon 20 long as a cheap, easy-to-find option. Drawback: standard tanks are rimmed, and Aquarium Store Depot calls the Aqueon 20 long not ideal for aquascaping. You also have to buy everything else separately.
2. 20-gallon starter kit — best budget. One box with the tank, hood, light, filter and often a heater is the quickest way to get started. Aquarium Store Depot's budget pick is the Aqueon 20-gallon kit, which it lists with a hood, power filter, heater, net, food and water conditioner. Drawback: in the same review the kit's heater is only "okay", the hood isn't ideal for plants, and it warns that kit filters are often undersized and cheap kit equipment often needs replacing within six months.
3. Rimless low-iron tank — best for planted aquascapes. With no plastic frame and clearer glass, a planted layout looks better from every side. Aquarium Store Depot's editor's choice is the UNS 60U, a rimless tank it says is well known in the planted community. Buce Plant lists it at 60 × 36 × 36 cm, 20.5 gallons, in 6 mm low-iron glass with a levelling mat included. Drawback: no filter, light or lid in the box, and Aquarium Store Depot says a UNS rimless tank needs a stand that supports it fully.
4. 20 high — best for tall fish or a narrow space. A 20 high holds the same water on a 24 × 12 inch footprint, which helps if you're short of space or keep tall fish. Aquarium Store Depot suggests it for vertical species such as juvenile angelfish. Drawback: less swimming length for most community fish, and at about 16 inches tall, more water depth for a planted-tank light to get through.
5. All-in-one with built-in filtration — best for hidden equipment. An all-in-one tank hides the filter in a walled-off back section, so there are no hoses or filter boxes on show. Aquarium Store Depot's example is the Waterbox 20 Cube, which it lists with a filter sock, bio-balls, carbon and sponge built in. Drawback: it's expensive next to a bare tank, the same review notes its black background may not suit planted scapes, and two of the other all-in-ones on its list are built for reef tanks.
My own tank
My planted community tank is a kit, but a little bigger than a 20 gallon: a Love Fish Vantage from Pets at Home, sold as 94 litres — about 25 US gallons. I still run the light it came with, three LED strips in blue and white, over two Amazon swords, an Anubias nana on a coconut shell and a Java fern on driftwood. The light has no dimmer or built-in timer, so I switch it with a GHome Smart plug, which I schedule from its app and can also control through Google Home. The tank came with its own filter and heater. I still use the heater, but I bought an OASE BioPlus 100 internal filter, which is more powerful than the filter supplied with the tank.
So a kit light can be enough for easy, low-light plants. For red or carpeting plants, the sources above point to a stronger light, which is where the best planted aquarium light shortlist comes in.
What you can skip
- Trusting the kit filter's size. Check its gallons-per-hour rating against Aquarium Store Depot's 150 minimum before you rely on it.
- A preset heater. Aquarium Store Depot says they can run 2–4°F hot; an adjustable one costs a little more.
- A rimless tank on a gappy cabinet. It needs a flat surface under the whole base.
- Buying "20 gallons" on volume alone. A long and a high hold the same water but suit different fish — choose the shape first.
Put it to work
Choosing the rest of the kit? See the best planted aquarium light for the light and the best canister filter if you want the filter hidden in the cabinet. The planted aquarium lighting guide covers how many hours to run it. Whatever tank you buy, cycle it before fish go in.