The short answer
No — do not use ordinary garden soil or potting compost in an aquarium. Both are made for pots and beds, not sealed underwater ecosystems. They typically contain added fertilisers, pesticides, wetting agents and organic matter that break down into ammonia and other pollutants, triggering algae blooms and poisoning fish. If you want a soil-based substrate, use a proper aquasoil instead.
Why garden soil is a problem
Under water, the ingredients that make garden products good for plants in the open air become hazards:
- Fertiliser — dissolves straight into the water column, spiking nitrate and phosphate and feeding algae.
- Pesticides and herbicides — can be toxic to fish, shrimp and snails.
- Organic matter and manure — decompose in the substrate, releasing ammonia and fouling the water.
- Wetting agents — surfactants added to compost are not meant to sit in a fish tank.
None of this is dosed or controlled the way an aquarium needs.
Safer alternatives
- Aquasoil — a purpose-made, nutrient-rich substrate that buffers pH slightly and grows plants beautifully. The simplest, safest route. Browse the substrate hub.
- Dirted tank (advanced) — a thin layer of plain, additive-free mineral topsoil capped with gravel or sand. This can work, but only with careful sourcing, mineralising and a fishless start-up to ride out the initial ammonia. Research it thoroughly before trying.
- Inert gravel or sand plus root tabs — no soil at all; you feed plants with fertiliser and root tabs from the fertiliser hub.
The bottom line
Garden soil belongs in the garden. For a planted aquarium, reach for aquasoil, or take the dirted route only with real caution. For setting plants in properly, see how to plant aquarium plants and aquascaping for beginners.