How to Use the Walstad Soil Calculator
The Walstad Method, developed by aquarist Diana Walstad and detailed in her book Ecology of the Planted Aquarium, uses a layer of organic potting soil beneath an inert sand cap to feed plants directly from their roots. The result is a low-maintenance planted tank that requires no CO₂ injection and minimal liquid fertilisers.
What Soil to Use
Use plain organic potting soil — the most common choices are Miracle-Gro Organic Choice or Scotts Premium Potting Mix. The critical requirement: no slow-release fertiliser pellets, no perlite, no moisture-retention crystals. These additives cause ammonia spikes and can kill fish. Plain organic soil only.
What Sand to Use
Any fine-grained, inert sand works. Pool filter sand (50-lb bags from hardware stores) is the most cost-effective choice. Avoid play sand with very fine particles that cloud easily. Aquarium-specific sands like CaribSea Super Naturals work well but cost more.
The Father Fish Method
Popularised by the Father Fish YouTube channel, this variation adds a thin mineral layer — typically crushed coral, lava rock pieces, and/or peat — beneath the organic soil. This mineral layer provides additional buffering, trace elements, and beneficial bacteria surfaces. The soil goes on top, then the sand cap as usual.