A planted aquarium scene: driftwood and fine green plants with a trail of oxygen bubbles rising toward warm light.

Vivariums · Walstad aquariums · living ponds

Most "self-sustaining" tanks sold online are sealed jars that die by spring.

A real one runs on soil, plants, and a cleanup crew doing the filtration, with a keeper who tops it off and prunes it. Closed Loop is how you build that: a 87-species compatibility database, a build planner, and 108 step-by-step guides.

Design your setup Start here
  • 41plants, with light and water needs
  • 34livestock species, parameter-matched
  • 30gear items, honestly rated

The honest version

A closed loop is a system whose waste feeds its own inputs.

Fish waste becomes plant food becomes clean water. A cleanup crew turns dead leaves into soil. Get the biology right and the system runs on plants and microfauna instead of a wall of equipment. It still needs you: a weekly top-off, a feeding, a prune. We do not sell the never-touch-it fantasy, because that jar is dead by month three.

Three ways to build one

Pick the system, and we will get you to a balanced build.

Walstad · low-tech Planted aquariums A dirted, no-filter tank that runs on soil, plants, and light. The Walstad method. Explore → Bioactive · dart frogs, geckos Vivariums & terrariums Live plants and a cleanup crew that turn waste into soil, so the enclosure runs itself. Explore → Outdoor · no filter Living ponds A balanced outdoor system where plants and biology hold the water clear without a pump. Explore →

The build planner

Tell it your water. It tells you what will balance.

Pick a setup type, a size, your light, and your water source, and the planner returns a stocked, planted build with a will-it-balance read: green, amber, or red, and the specific reason. It computes on the same 87 records the database renders from, so the temperature and pH ranges are real, not guessed.

Open the build planner

The compatibility database

Settle a compatibility question in thirty seconds.

Every plant, fish, shrimp, snail, cleanup-crew invertebrate, and piece of gear, with the parameters that decide whether two of them can share a system. This is the fact spine: when a guide states a range, it comes from a record here.

Browse the database
  • 41 plants
  • 34 livestock
  • 12 microfauna
  • 30 gear

The eight topics

Everything, in order.

Self-Sustaining Planted Aquariums Low-tech, dirted, no-filter tanks that run on soil, plants, and light (the Walstad method). Bioactive Vivariums & Terrariums Live plants and a cleanup crew that turn waste into soil, so the enclosure runs itself. Living Ponds Balanced outdoor systems where plants and biology hold the water clear without a pump. Plant & Species Compatibility What lives with what, at which parameters, and where two choices collide. Water Chemistry & the Nitrogen Cycle The biology that does the filtration: cycling, pH, hardness, ammonia to nitrate. Getting Started & Build Guides Step-by-step first builds by setup type and size, from a 2-gallon jar up. Troubleshooting Algae, cloudy water, plant melt, stalled cycles, and die-off: what causes each and the fix. The Database & Planner How to use the compatibility database and the build planner, and what the numbers mean.

Why we build these

Decay is not the system failing. It is the system working: the same turn that makes a fallen log the seedbed for the next tree.

A closed loop turns waste into food and death into soil. Build a single 10-gallon jar of water, plants, and soil and you hold the smallest honest model of an ecosystem in two hands, running by the same rules as the yard, the watershed, and the planet.

Read the philosophy →

One build breakdown a week.

A stocked, balanced setup pulled apart: the plants, the cleanup crew, the parameters, and where it would go wrong. Free.

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