Walstad tanks are a type of aquarium setup that is designed to mimic a natural ecosystem. The method, developed by microbiologist Diana Walstad, involves using a substrate of organic potting soil, capped with gravel or sand, to create a nutrient-rich environment for plants and beneficial bacteria to grow.
In a Walstad tank, the plants and the beneficial bacteria that live in the substrate work together to maintain water quality and create a self-sustaining ecosystem. The goal (and the beauty!) is to have a balanced and stable environment where aquatic life can thrive without the need for artificial filtration or frequent water changes.
I stumbled onto the Walstad method in 2017 and have created multiple of such tanks, to varying degrees of success.
A betta fish tank I set up in 2021. No filters, dirted and heavily planted, in accordance with the Walstad method.
Inhabitants included a Mexican crayfish, micro rasboras, a sparkling gourami and my Khuli loaches.
Diana Walstad's method is based on the idea that an aquarium can be viewed as a small-scale ecosystem, and that by creating the right conditions, processes we observe in larger ecosystems can be harnessed in our micro-environment to maintain water quality and support plant and animal life. Other than feeding the aquatic animals and topping up water that has been lost from evaporation, little else should be required to maintain these tanks.
The substrate used in Walstad tanks is typically a layer of organic potting soil capped with a layer of sand or gravel. The potting soil provides a source of nutrients for the plants, and contains decomposing organic matter that is broken down by beneficial bacteria.
The decomposition of organic matter in the substrate releases nutrients, such as nitrogen and phosphorus, into the water. These nutrients are taken up by the plants, which use them to grow and thrive. As the plants grow, they absorb more nutrients, which in turn reduces the amount of nutrients available to algae and other unwanted organisms.
The substrate in Walstad tanks is also home to a variety of beneficial bacteria, which play a critical role in maintaining water quality. These bacteria break down organic waste, such as fish waste and excess food, into less harmful compounds that can be absorbed by the plants. The bacteria also convert harmful ammonia into less toxic compounds, such as nitrate, which can be used by the plants as a nutrient source.
The plants in a Walstad tank play a vital role in maintaining water quality and supporting animal life. Through photosynthesis, the plants release oxygen into the water, which is essential for the health of fish and other aquatic animals. The plants also absorb carbon dioxide, which helps to regulate the pH of the water and prevent fluctuations that can be harmful to aquatic life.