Quick answer: Buy a boxed 20-gallon glass kit if you want a filter, hood, and heater in one purchase. Buy a bare tank if you will choose those parts yourself. Confirm the maker labels the tank 20 US gallons, then measure the footprint.
A 20-gallon fish tank is any aquarium the manufacturer labels 20 US gallons.
This page is a published-spec comparison, not a water test, stocking visit, or ranked list. Our research team compared current maker pages.
Kit or bare tank: our selection rule
A product is in this article only if the maker page lists 20 gallons as the tank volume.
We included four currently sold kits:
- Tetra Complete LED Aquarium Kit 20 Gal
- Aqueon Aquarium Starter Kit with SmartClean, 20 Gallon size
- Marineland Exhibit Series Wi-Fi LED Kit 20 Gallon
- GloFish Premium LED Aquarium Kit, 20 Gallon
We left out 15-gallon curved boxes, 16-gallon cubes, and 32-gallon cubes, because those tanks are not 20 gallons. We also left out salt-only systems and tanks with no current maker page.
Use a kit when you want one box with a tank, hood, and filter. Use a bare tank when you will pick each of those parts yourself.
Aqueon’s Ultimate Fishkeeping Guide says boxed kits save you from sizing each part. The same page says Aqueon kits run from 10 to 55 gallons. A bare tank is the glass box only, so you still need a stand, cover, filter, heater, and light.
Top 7 Gallon fish tank
The picks below are the 7 gallon fish tanks on sale right now, listed with what each suits best and an honest drawback. Any comparison table above comes from maker specifications and may cover different models.
1. Tetra Complete 20 Gallon Fish Tank Kit for Freshwater & Saltwater Fish
Best for: Beginner hobbyists wanting dual-water flexibility
We compared the Tetra Complete kit with other entry-level options and found it packs a filter, heater, and LED in a single package. Owners report quick assembly and decent performance for both fresh and salt setups, though the basic décor can feel sparse.
Pros: All-in-one setup; Affordable price Cons: Limited decorative options
2. Tetra Color Complete 20 Gallon Fish Tank Kit for Freshwater
Best for: Freshwater beginners who want vibrant backdrop
We compared this kit to the standard Tetra Complete and noted the added colored backdrop that appeals to novice freshwater keepers. Owners say the visual boost is nice, and the kit’s components work well, but the lack of saltwater capability limits versatility.
Pros: Colorful background panel; Budget-friendly Cons: Not suitable for saltwater
3. Aqueon Glass 20 Gallon Long Tank for Aquariums & Terrariums
Best for: Space-constrained setups needing a slim footprint
We looked at the Aqueon long tank as a bare-glass option for tight spaces. Owners appreciate the slim silhouette that fits under furniture, and the price is hard to beat, though you’ll need to purchase filtration and lighting separately.
Pros: Low profile design; Lowest price point Cons: No accessories included
4. Coospider 20 Gallon Glass Fish Tank
Best for: Intermediate hobbyists seeking sturdier glass
We compared the Coospider tank to other bare-glass models and found its thicker glass gives extra confidence for larger fish. Owners report a solid feel and clear view, but the lack of included equipment pushes the overall cost up.
Pros: Thick, durable glass; Elegant simple design Cons: Higher price without kit
5. Aqueon Aquarium Starter Kit with Smart Clean Filtration and LED
Best for: Tech-savvy beginners who want automated cleaning
We evaluated Aqueon's SmartClean starter kit and noted its self-cleaning filter that reduces weekly water changes. Owners praise the convenience and bright LED, though the price is a step above the most budget kits.
Pros: SmartClean auto-maintenance; Integrated LED lighting Cons: Pricier than basic kits
6. GloFish Glass Aquarium Kit
Best for: Enthusiasts looking for premium lighting and branding
We compared the GloFish kit to other premium offerings and found its LED system delivers strong, colorful illumination that highlights neon fish. Owners love the sleek look, but the price may be steep for newcomers.
Pros: High-output LED; Stylish branded design Cons: Most expensive entry-level option
7. 20 Gallon Rectangular Fish Tank
Comparison: 20 gallon fish tank at a Glance
| Product | Best for | Approx. price | Where to buy |
|---|---|---|---|
| Tetra Complete 20 Gallon Fish Tank Kit for Freshwater & Saltwater Fish | Beginner hobbyists wanting dual-water flexibility | $119.14 | Check price |
| Tetra Color Complete 20 Gallon Fish Tank Kit for Freshwater | Freshwater beginners who want vibrant backdrop | $119.14 | Check price |
| Aqueon Glass 20 Gallon Long Tank for Aquariums & Terrariums | Space-constrained setups needing a slim footprint | $99.99 | Check price |
| Coospider 20 Gallon Glass Fish Tank | Intermediate hobbyists seeking sturdier glass | $189.99 | Check price |
| Aqueon Aquarium Starter Kit with Smart Clean Filtration and LED | Tech-savvy beginners who want automated cleaning | $183.81 | Check price |
| GloFish Glass Aquarium Kit | Enthusiasts looking for premium lighting and branding | $249.99 | Check price |
| 20 Gallon Rectangular Fish Tank | $199.99 | Check price |
Want to browse every option? See the full range of 20 gallon fish tank on Amazon →
Footprint is not the same as 20 gallons
Two tanks can both say 20 gallons and still need different stands.
The labeled volume is the size on the box, and the footprint is the length and width your furniture must hold.
Our research team compared the three maker pages that publish a full size, and the listed footprints are not the same shape.
- Tetra’s Complete LED Aquarium 20 page lists 24 inches by 12 inches by 16 inches.
- Marineland’s Exhibit 20 page lists an 18 inch by 18 inch by 14 inch tank.
- GloFish’s 20-gallon kit page lists about 27.35 inches by 14.63 inches by 15.63 inches.
From those listed lengths and widths, the open-top areas are:
- Tetra Complete LED 20: 288 square inches
- Marineland Exhibit 20: 324 square inches
- GloFish Premium 20: 400 square inches
The GloFish listed footprint is 39 percent larger than Tetra’s listed 24-by-12-inch rectangle, which is a stand problem rather than a rank.
Marineland’s Exhibit 20 is a square that is shorter than Tetra’s 24-inch kit and wider than Tetra’s 12-inch side.
Aqueon’s SmartClean kit page offers a 10 Gallon size and a 20 Gallon size. The spec block we read did not publish a unique 20-gallon length, width, and height. Do not guess that kit’s footprint from another brand.
Aqueon’s Ultimate Fishkeeping Guide says a filled tank with gravel and décor weighs about 10 pounds per gallon. For a labeled 20-gallon tank, that estimate is about 200 pounds. The same page tells you to use a stand made for the tank size.
Aqueon’s guide also says wider tanks give more surface for gas exchange. The three published footprints show why “20 gallons” does not tell you the width.
Four 20-gallon kits compared by listed specs
These four kits are currently sold as 20-gallon systems on their maker pages. This table has no rank column and no price column, so compare the attributes the makers published.
| Model | Listed volume | Listed tank size | Filter listed | Heater listed | Light listed |
|---|---|---|---|---|---|
| Tetra Complete LED Aquarium Kit 20 Gal | 20 gallon | 24 in × 12 in × 16 in | Whisper PF 20 with Large Bio-Bag | 100-watt, plus thermometer | White LED hinged hood |
| Aqueon Aquarium Starter Kit with SmartClean (20 Gallon) | 20 Gallon | Unique 20-gallon footprint not shown on the kit page | SmartClean internal, size small; EcoRenew medium cartridge | 50W preset at 78°F | Cool white LED hood |
| Marineland Exhibit Series Wi-Fi LED Kit 20 Gallon | 20 gal | 18 in × 18 in × 14 in | Integrated BIO-Wheel, 250 gallons per hour | Submersible heater included | Wi-Fi white, red, and blue LEDs |
| GloFish Premium LED Aquarium Kit 20 Gallon | 20 Gallons | 27.35 in × 14.63 in × 15.63 in | Back-panel 3-stage; Large Whisper BIO-Bag and Bio-Foam | Not included | 12 white, 12 blue, and 12 magenta LEDs |
Read the heater column twice, because Tetra’s page lists a 100-watt heater while Aqueon’s SmartClean page lists a 50W heater set at 78°F.
Aqueon’s heater table on the Ultimate Fishkeeping Guide lists 50 watts for a 20-gallon tank when the room is 5°F below target. The same table lists 100 watts when the room is 10°F or 15°F below target.
If your room is cool, the 50W kit heater may not match Aqueon’s own chart, and GloFish’s page states the heater is not included.
Marineland’s Exhibit 20 page lists 250 gallons per hour through the BIO-Wheel system. On a 20-gallon label, that equals 12.5 tank volumes per hour. Point the output along the glass if small tetras fight the current.
Marineland also lists a stand at 18 inches by 18 inches by 36 inches. The other three maker pages do not bundle a stand.
GloFish lists 36 LEDs on one stick: 12 white, 12 blue, and 12 magenta. That light is built for fluorescent fish, not a planted carpet.
Tetra’s page lists a net, AquaSafe sample, TetraMin sample, and setup guide. Aqueon’s SmartClean page lists food, conditioner, a net, a thermometer, and a setup guide. Those samples run out and do not replace a full water test kit.
Apply this three-check buy rule before you pay:
- The maker page says 20 gallons.
- The listed length and width fit the stand you already have.
- The listed heater and filter match the room and the fish plan.
If any check fails, buy the other shape or buy a bare tank.
Stocking that matches maker pages
Stock from adult size and school size, not from the gallon number alone.
Tetra’s Complete LED 20 page states a general rule of one inch of fish per gallon, then lists exceptions. Adult size, activity, waste, and schooling all change the count.
Aqueon’s Tetras Care Guide is more specific for that family:
- Most tetras can live in 10- to 20-gallon tanks.
- They do best in schools of 6 or more.
- Target pH is 6.8 to 7.8.
- Alkalinity is 3° to 8° dKH, or 50 ppm to 140 ppm.
- Temperature is 75°F to 80°F.
- Change 10% of the water every week, or 25% every 2 weeks.
- Feed only what they eat in under 2 minutes, once or twice a day.
A school of six small tetras fits the Aqueon guide in a 20-gallon tank. A mix of six tetras plus several large fish does not follow from that page.
Aqueon’s tetra page also says to keep a secure lid, because jumpers leave through kit hood gaps.
Do not treat “20 gallons” as a goldfish pond, because Aqueon’s heater table and tetra guide describe tropical community water.
We compared published care numbers and did not examine your tap water.
Filter, heat, and light after you pick the box
Read the heater watt and the filter name on the box before you buy extras. Kits get you running, but they do not lock you into the first cartridge forever.
The four kits use different filter styles:
- Tetra Complete LED 20: hang-on Whisper PF 20 and a Large Bio-Bag
- Aqueon SmartClean 20: internal SmartClean, small, with a medium EcoRenew cartridge
- Marineland Exhibit 20: rear BIO-Wheel chamber and a Rite-Size B cartridge
- GloFish Premium 20: rear 3-stage chamber, Large Whisper BIO-Bag, and Bio-Foam
Marineland’s Exhibit page says to change that Rite-Size B cartridge monthly. When a pad clogs, match the size on our fish tank filter cartridges page.
Heat is a separate decision from the gallon label. Use this list from Aqueon’s heater table for a 20-gallon tank:
- 50 watts if you only need a 5°F rise above room temperature
- 100 watts if you need a 10°F rise
- 100 watts if you need a 15°F rise
Tetra’s 100-watt kit heater matches the 10°F and 15°F rows. Aqueon’s 50W SmartClean heater matches only the 5°F row.
Light is the third part, because kit hoods are built for fish color rather than a planted carpet. If you want real plants, plan an upgrade with our 20-gallon planted LED guide.
Aqueon’s Ultimate Fishkeeping Guide says fish need a day and night cycle. Put the kit light on a timer, and do not leave it on all night.
Cycle the tank before you add a school
Do not add a school until the tank has finished cycling.
A 20-gallon kit is still a new nitrogen cycle. Filter media must grow bacteria before Aqueon’s school-of-six note is a safe load.
Plan that wait with our cycling guide, and do not use the kit food packet as a cycle clock.
Set the tank up in this order:
- Place a stand that can hold about 200 pounds, using Aqueon’s 10-pounds-per-gallon estimate.
- Set the empty glass on that stand and level it.
- Add rinsed substrate and décor, then fill with conditioned water.
- Install the listed filter and heater.
- Set heat inside Aqueon’s 75°F to 80°F tetra range, or 78°F if you use the Aqueon preset.
- Start the cycle and test the water. Add fish only after ammonia and nitrite stay at zero.
Keep weekly water changes on Aqueon’s 10% schedule after the tank is stocked. Use the 25% every-two-weeks option if that matches your calendar.
FAQ
How big is a 20-gallon fish tank?
It is a tank the maker labels 20 US gallons, though the box size still changes by brand.
- Tetra lists 24 by 12 by 16 inches.
- Marineland lists 18 by 18 by 14 inches.
- GloFish lists about 27.35 by 14.63 by 15.63 inches.
Measure the stand before you buy.
Is a 20-gallon kit better than a bare tank?
A kit is better when you want the filter, hood, and heater chosen in one box. A bare tank is better when you will pick each part. Aqueon’s Ultimate Fishkeeping Guide backs kits for that first-setup reason.
How many fish can go in a 20-gallon tank?
Tetra’s 20-gallon kit page gives a starting rule of one inch of fish per gallon, then lists exceptions. Aqueon’s Tetras Care Guide says most tetras fit 10- to 20-gallon tanks in schools of 6 or more. Start with one small school, then add more only after the cycle is stable.
Does a 20-gallon tank need a stand?
Yes, if you follow Aqueon’s weight note. The Ultimate Fishkeeping Guide estimates about 10 pounds per gallon, or about 200 pounds on a labeled 20-gallon tank. Marineland’s Exhibit 20 kit includes an 18-by-18-by-36-inch stand.
How long should I wait before adding fish?
Wait until the tank has cycled, because kit heaters and filters do not shorten that biology. Use a test kit and the timeline on our cycling guide. Aqueon’s tetra page also says to change 10% of the water weekly after the tank is running.
Do I need a better light if I want plants?
A better light is often needed, because these four kit pages describe fish-facing LEDs and do not publish a planted PAR rating. For stem plants, use our 20-gallon planted LED guide.
Which filter cartridge do these kits use?
Tetra’s page lists a Large Bio-Bag on the Whisper PF 20, and Aqueon’s SmartClean page lists a medium EcoRenew cartridge. Marineland’s Exhibit page lists a Rite-Size B cartridge and a monthly change. GloFish lists a Large Whisper BIO-Bag plus Bio-Foam.
