How much substrate do I need for a 20 gallon long tank?

For a 76 x 30 cm footprint at a 3 inch average depth you need about 18 litres: roughly 18 kg of aqua soil or 27 kg of sand. At 2 inches it is 12 litres.

What size heater for a 20 gallon long planted tank?

A 50 W heater. Once substrate and rock are in, a 20 gallon long holds about 50 litres (13.3 gallons) of water, which works out to 3.8 W per gallon.

How much filter flow does a 20 gallon long planted tank need?

Aim for 200-300 litres per hour, which turns the water over 4 to 6 times an hour. Planted tanks like steady, gentle flow rather than a jet.

Is a 20 long better than a 20 high for plants?

Usually yes. The 20 long is 12 inches tall, so light reaches the bottom at full strength and carpet plants grow without high-output lighting.

20 gallon long planted tank setup

Shallow and wide, which is exactly what plants want: light reaches the substrate easily and the 30 inch length gives you room for a real layout.

Dimensions: 76x30x30 cm; 30 x 12 x 12 in outer
Water volume: 50 L; 71 L (18.7 gal) gross, less substrate and rock
Substrate, 3 in average: 18 L; 18 kg aqua soil or 27 kg sand
Heater: 50 W; 3.8 W per gallon
Filter flow: 200-300; litres per hour, 4-6x turnover
Light timer: 6-7 hours; without CO2

Lighting

A 76 cm tank needs a bar that covers the full length so the ends do not go dark.

Fits this tank

Aurora Smart 78 — RGB App-Controlled LED

78 cm bar, fits 70 to 95 cm tanks; your tank is 76 cm long.

$80

Filtration

Target 200-300 L/h for a planted tank this size.

Right-sized filter

Hang-On-Back Waterfall Filter — 3-Stage, 250 L/H

250 L/h hang-on-back, rated for tanks up to about 80 L.

$17

CO2

Optional. Low-light plants grow without it; add CO2 if you want a carpet or red stems.

CO2 option

DIY CO2 Generator Kit — 2 L Stainless

Refill-free citric acid kit; enough for a tank this size without a gas cylinder.

$66

Substrate by depth

Slope it: shallower at the front glass, deeper at the back. The average depth is what sets how much you buy.

2 in average

12 L

12 kg soil, 18 kg sand

3 in average

18 L

18 kg soil, 27 kg sand

4 in average

24 L

24 kg soil, 35 kg sand

Custom tank? Use the substrate calculator

What to plant

Suits: Nature aquarium with a sloped hardscape, or a shallow riverbank scape.

Monte Carlo or dwarf hairgrass carpet (CO2 helps)
Staurogyne repens in the midground
Ludwigia and Rotala stems at the back
Floating red root floaters to shade shy fish

Fish and shrimp

A school of 12 ember tetras or harlequin rasboras, a group of pygmy corydoras on sand, and shrimp for clean-up.

Mistakes that cost people this tank

1Choosing a 60 cm light. The tank is 76 cm long, so a short bar leaves dark ends; use a bar that fits 70 to 95 cm.
2Under-sloping. A shallow tank looks flat unless the substrate rises 2 inches from front to back.
3Heater placement. Put it near the filter outflow so warm water reaches both ends of a long tank.

Quick answers

How much substrate do I need for a 20 gallon long tank?: For a 76 x 30 cm footprint at a 3 inch average depth you need about 18 litres: roughly 18 kg of aqua soil or 27 kg of sand. At 2 inches it is 12 litres.
What size heater for a 20 gallon long planted tank?: A 50 W heater. Once substrate and rock are in, a 20 gallon long holds about 50 litres (13.3 gallons) of water, which works out to 3.8 W per gallon.
How much filter flow does a 20 gallon long planted tank need?: Aim for 200-300 litres per hour, which turns the water over 4 to 6 times an hour. Planted tanks like steady, gentle flow rather than a jet.
Is a 20 long better than a 20 high for plants?: Usually yes. The 20 long is 12 inches tall, so light reaches the bottom at full strength and carpet plants grow without high-output lighting.