Aquaponics Fish Tank: How to Choose One and Set It Up

An aquaponics fish tank is the half of the system that holds the fish, and it decides almost everything else: how many fish you can keep, how much plant growing area they can feed, and where the whole thing can sit. Any tank that is watertight, safe for fish and big enough will do. Indoors that usually means a glass aquarium of 10 to 29 gallons with a grow bed on top; outdoors and in garages it means a poly stock tank or an IBC tote.

This guide covers how to choose an aquaponics tank, the three tanks we would buy for it, and the three ways to turn a fish tank you already own into a small aquaponic garden. If you would rather buy the whole system in one box, our guide to the best aquaponics kits compares the complete ones.

What Makes a Good Aquaponics Fish Tank

Four things matter, in this order: volume, material, shape and light. Looks come last, though for an indoor tank they are often the reason to do aquaponics at all.

Volume: Size the Tank to the Fish

Rutgers Cooperative Extension's fact sheet FS1351, an introduction to aquaponics systems, sizes fish tanks at about 10 gallons of water for every pound of fish at maturity or harvest size. That rule is the quickest way to see what a tank can do. A 10 gallon aquarium carries about a pound of adult fish in total, a few small tropicals or one goldfish at most. A 50 gallon stock tank carries around five pounds, which starts to feed a real grow bed. Fish you plan to eat, such as tilapia, belong in 100 gallons or more.

Bigger is also more forgiving. A small volume of water changes temperature and chemistry quickly, so a missed feeding or a dead snail shows up in a day. In a large tank the same mistake is diluted.

Material: Food-Safe and Fish-Safe

Clemson Cooperative Extension's guide to aquaponics system layout (Lance Beecher, 2021) lists the dependable tank materials as polypropylene, high-density polyethylene and fiberglass for preformed tanks, with PVC or EPDM liners for tanks you build. Glass is the indoor standard. The same guide warns that a recycled tank is often the cheapest choice but that you need to know its history, because a container that held chemicals can poison fish years later.

Shape: Round Beats Square

Rutgers prefers circular, oval or multisided tanks, because water circulates without dead corners and fish waste does not settle where the pump cannot reach it. If you use a rectangle, pick one with rounded edges. For an aquarium indoors this matters less, since you are keeping few fish and can siphon the gravel; for a stock tank outdoors, the oval shape is a quiet advantage.

Light: Fish Like Shade, Algae Likes Sun

A clear tank in sunlight grows algae fast, which competes with your plants for nutrients and clouds the view. Indoors, keep a glass aquarium out of direct sun, or put a background on its back and sides. Outdoors, opaque tanks and a cover over part of the surface keep the water cooler and the algae down.

Types of Aquaponics Fish Tanks

Desktop tanks are covered in our guides to aquaponics kits and the self-cleaning fish tank, and IBC totes have their own guide to IBC aquaponics. This page focuses on the first and third rows: the tanks people actually build around.

Best Fish Tanks for Aquaponics

All three are standard tanks sold for fish or livestock, not aquaponics, which is the point: they are cheap for their size, easy to replace and made to hold water for years.

Tetra LED 10 Gallon Complete Fish Tank Kit (Best Indoor Start)

A 10 gallon tank is where most indoor aquaponics starts, because the ready-made grow beds, the AquaSprouts Garden among them, are built for its standard 20 by 10 by 12 inch footprint, and Tetra's listing gives exactly those dimensions. The kit adds a low-profile hinged hood with LED lighting, an internal filter with cartridge, and samples of water conditioner and food.

For aquaponics you use the tank and keep the rest in a drawer for now: the grow bed replaces the hood, and once the bed is cycled the plants and the bacteria in its media take over most of the filter's job. The filter is still worth running for the first weeks while the bacteria establish. Ten gallons limits you to a few small fish such as guppies, platies or white cloud minnows, which is plenty to feed a bed of herbs.

Best for: a first aquarium-top system. Missing: a grow bed, a heater for tropical fish, and a grow light unless the tank sits by a bright window.

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Tetra ColorFusion 20 Gallon Complete Aquarium Kit

Twenty gallons doubles the fish you can carry and gives a homemade grow bed more room to work. Tetra's listing names a 20 gallon glass aquarium with hood, a UL heater, a Whisper 20 filter, a color-changing LED and decor: two plant multipacks and an anemone. The heater is the useful part for aquaponics, since most of the small fish that suit a tank this size are tropical.

No ready-made aquaponics bed is sold for a 20 gallon footprint, so this is the tank for a build: a plastic tray or planter box with clay pebbles over the rim, fed by a small pump. The listed dimensions, 27.88 by 16.13 by 20.38 inches, are the overall kit size, so measure the glass itself before you cut a bed to fit. The color-changing light is decoration, not a plant light.

Best for: a larger indoor tank with a homemade bed. Missing: the grow bed, a plant light and the plants.

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Rubbermaid Brute 50 Gallon Stock Tank

Stock tanks are the classic step up from an aquarium: tough, made to hold drinking water for animals outdoors, and shaped for easy cleaning. Rubbermaid's Brute is made in the USA from structural foam, carries a 10-year limited warranty, and the 50 gallon model is a shallow 12 inches deep on a 52 by 31 inch footprint. That shallow shape is a double use: as a fish tank it suits a modest stock of goldfish or similar hardy fish, and the same tank also works as a wide grow bed set over a deeper fish tank.

Plan a stand or a bed beside it, a pump sized for the lift to your grow bed, and a cover over part of the surface to keep sun and leaves out. For more depth, Rubbermaid lists the Brute in 100 and 150 gallon sizes as well.

Best for: a garage, patio or greenhouse system. Missing: grow bed, pump, plumbing and a cover.

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How to Turn a Fish Tank Into an Aquaponics System

If you already keep an aquarium, you are most of the way there. These are the three conversions, from the simplest to the most productive. All three need a cycled tank, so if the tank is new, read our guide to fishless cycling first.

Option 1: Hang-On Planters

The quickest version, and the answer to the classic betta fish tank with plants on top, is a planter that hooks over the rim so a plant's roots trail into the water. Pothos, lucky bamboo, peace lily and spider plant cuttings are the usual choices because they root in water and do not mind low light. Each plant takes up a little nitrate, the end product of fish waste, which slows how fast it builds up between water changes. It is aquaponics in miniature: it helps, but it does not replace changing water.

Borlech Large Aquarium Plant Holder (2 Pack)

A slotted plastic cup, 3.54 by 3.54 by 3.94 inches, that hooks over the tank edge (three hook sizes for glass or rims up to 1.57 inches) or sticks to the glass with suction cups. The slots let water flow through the roots, and the cup keeps fish from nibbling them. Sold with a houseplant cutting in mind, so it suits pothos and similar plants that grow out of the top of the tank.

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Carpetsma Glass Aquarium Plant Pot

A small glass pot, 2.4 inches square, that hangs on the inside of the glass with two suction cups and has drainage holes in the base. It is sized for aquatic and semi-aquatic plants that live in or at the waterline rather than houseplants, so it is the better pick for a planted look than for growing anything to eat.

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Option 2: A Raft Lid With Net Cups

Cut a lid from acrylic or rigid foam to sit on the rim, drill holes for 2 or 3 inch net cups, and fill the cups with clay pebbles around each seedling. The roots hang straight into the tank water. This is a raft system, the same idea commercial growers use for lettuce, scaled down to an aquarium. It works well for leafy herbs, lettuce and watercress. Two rules make it work: run an air stone, because roots and fish now share the oxygen, and keep the fish load light, because there is no media bed filtering the water.

Option 3: A Pumped Grow Bed on Top

The most productive version sets a tray of grow media over the tank and pumps tank water up into it. The water trickles through the media, where bacteria convert the waste, and drains back down. A timer or a bell siphon lets the bed flood and drain so roots get air between waterings. You can buy this ready-made for a 10 gallon tank (the AquaSprouts Garden in our kits guide) or build it from a planter box, a small submersible pump and clay pebbles. SRAC publication 454 by Rakocy, Masser and Losordo recommends about 1 cubic foot of fish tank per 2 cubic feet of gravel in flood and drain systems. On an aquarium the bed is almost always smaller than that, which is fine: it simply means fewer fish and a lighter feeding schedule.

Setting Up, Step by Step

Whatever the option, the order is the same. Set up the tank and the bed or planters. Run the water and cycle it until ammonia and nitrite read zero and nitrate appears. Plant. Add a few fish, then more over the following weeks while you test. Keep the pH close to 7, the compromise SRAC 454 gives between the needs of the bacteria and the plants, and keep the tank out of direct sun.

Fish for an Aquaponics Fish Tank

Match the fish to the tank, not the other way round. In a 10 gallon aquarium, small hardy community fish such as guppies, platies, white cloud minnows or a single betta are the realistic choices. Goldfish produce a lot of waste, which plants like, but they grow large and need far more water than a small aquarium offers. Tilapia, perch, bluegill and catfish are stock tank and IBC fish. Our guides to the best fish for aquaponics and aquaponics tilapia go species by species, and the best plants for aquaponics guide covers what to grow over them.

What You Need to Convert an Aquarium

For options 2 and 3: a pump, cups, media and a way to see what the water is doing.

1. 

   1Pump

   PULACO 160 GPH Submersible Pump

   An adjustable small pump with a maximum lift of 4 feet, enough to raise water from a 10 or 20 gallon tank into a bed on top.

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2. 

   2Net cups

   ORIMERC 3 Inch Net Cups (12 Pack)

   Slotted cups with a wide lip that will not drop through the holes in a raft lid.

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3. 

   3Grow media

   Halatool Leca Clay Pebbles (2 lb)

   Light, pH-neutral expanded clay for the cups or a small bed. Rinse before use.

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4. 

   4Water tests

   API Freshwater Master Test Kit

   pH, ammonia, nitrite and nitrate: the readings that tell you the tank has cycled and the fish are safe.

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