The Best 20-Gallon Tank Setup: Every Piece of Gear
A complete 20-gallon aquarium setup: which heater, filter, light, conditioner and test kit to buy, and the order to install and cycle it.
A good 20-gallon setup needs a 100-watt heater, a filter rated a little above 20 gallons (a hang-on-back is easiest), a 24-inch light matched to whether you keep plants, water conditioner and a liquid test kit. Buy all of it before any fish, then cycle the tank first. A 20-gallon is the size most experienced keepers recommend to start with, because the larger water volume is far more forgiving of beginner mistakes than a 5 or 10.
Why a 20-gallon is the size to start with
If you are choosing your first tank, a 20-gallon is the sweet spot. The extra water volume over a 5 or 10-gallon dilutes mistakes, holds temperature more steadily, and gives you a real choice of fish. The gear below is what turns an empty 20-gallon into a stable, cyclable tank.
Here is the whole shopping list, then the reasoning for each piece.
| Gear | Our pick | Why |
|---|---|---|
| Heater | Eheim Jager 100W | Accurate, recalibratable |
| Filter | Seachem Tidal 35 | Bulk media, easy to service |
| Light | NICREW ClassicLED Plus 24-30 in | Fits a 24-inch tank, full spectrum |
| Conditioner | Seachem Prime | One capful treats 50 gallons |
| Test kit | API Freshwater Master Kit | Liquid reagents, real numbers |
The heater: 100 watts
A 20-gallon in a normally heated room wants about 100 watts to hold a stable tropical temperature. The Eheim Jager 100W is the default because it is accurate to within a degree and its dial can be recalibrated, which is rare at this price. If your room runs cold, size up using our heater wattage calculator.
The filter: a hang-on-back rated above the tank
Buy a filter rated a little above your tank, not exactly at it, so it is not working flat out. The Seachem Tidal 35 is our top-ranked HOB because it takes bulk media in a large basket instead of locking you into proprietary cartridges, and it self-primes. A HOB is the easiest filter type to live with on a tank this size.
The light: match it to your plants
This is the one piece that depends on your plans. A standard 20-gallon "high" is 24 inches long, so a 24-inch fixture fits.
- Fish only, or easy plants: the NICREW ClassicLED Plus is plenty and inexpensive.
- A properly planted tank: step up to a stronger fixture, covered in our planted-tank light guide.
Put the light on a timer for 6 to 8 hours a day. Longer runs mainly grow algae, not plants.
The unglamorous two: conditioner and test kit
These are the pieces beginners skip and regret. Seachem Prime neutralises chlorine and chloramine in tap water and is overdose-safe, so a beginner mistake stays harmless. The API Freshwater Master Test Kit uses liquid reagents that give real numbers, which you need to see the tank through its cycle.
The order that matters
Buy everything, install it, then cycle the tank with no fish in it. Cycling grows the bacteria that make the filter actually filter, and it takes a few weeks. Skipping it is the single most common reason a first tank crashes. Follow our fishless cycling guide, and only then add fish, a few at a time.
For a standard 20-gallon: a 100-watt Eheim Jager heater, a Seachem Tidal 35 hang-on-back filter, a 24-inch NICREW ClassicLED Plus, Seachem Prime conditioner and the API Freshwater Master Test Kit. Buy the gear first, cycle the tank, then stock slowly.
Common questions
How much does a 20-gallon setup cost?
The equipment in this guide (heater, HOB filter, light, conditioner and a master test kit) comes to roughly 180 dollars at the prices we track, before the tank and stand themselves. You can cut that by choosing budget picks in each category, but the test kit and conditioner are not the place to save.
What size heater does a 20-gallon need?
About 100 watts for a room that stays near normal house temperature. If the room gets cold in winter you may want a little more headroom. Our heater wattage calculator sizes it from your tank volume and how cold the room actually gets.
Do I need a filter and a heater and a light?
A filter and heater, yes, for a tropical community tank. A light is only strictly needed if you keep live plants or simply want to see the fish; fish themselves do not require bright light and are calmer without a harsh one.