Aquarium substrate: sand, gravel, or aquasoil
Substrate choice shapes plant root health, water clarity, and the wellbeing of bottom-dwelling fish. We break down the three options.
Substrate isn't a 'decorative underlay' — it's a biological filter and a structural base for rooted plants. The right choice shapes plant health, bottom-fish behaviour, and water clarity.
Three main types
Sand (0.5–2 mm)
Ideal for corydoras, loaches, and other species that sift the substrate — it's natural behaviour for them. Downsides: compacts over time, can go anaerobic in deeper zones. Rooted plants struggle in pure sand without supplements.
Gravel (2–5 mm)
The universal choice for community tanks. Doesn't compact, vacuums easily with a siphon. Rooted plants grow moderately well — residual organic matter provides base nutrition without fertiliser.
Aquasoil (nutrient substrate)
Baked clay granules (ADA Amazonia, Tropica Aquarium Soil, Fluval Stratum, etc.) with high cation exchange capacity. Drops pH by 1–1.5 units, packed with nutrients. Expensive but essential for demanding plants: HC Cuba, hairgrass, Rotala wallichii.
Layer depth
4–6 cm for rooted plants; 2–3 cm for epiphyte-only setups (anubias, fern) or no-plant tanks. Too thin and roots can't anchor; too deep and the lower layer goes anaerobic.
Colour and aesthetics
Light substrate visually enlarges the tank but fish look paler (protective coloration response). Dark substrate intensifies fish colours and hides leftover food and waste better.
What to avoid
• Sharp crushed gravel — injures corydoras barbels and the bellies of bottom fish. • Painted coloured substrates — coating peels off over time and leaches into the water. • Limestone or coral chips — raise pH and kH irreversibly; unsuitable for freshwater.
A substrate lasts 5–10 years. Far better to choose well once than to redo it after a year because of a bad start.
FAQ
- Can I mix sand and gravel?
- Yes, but the coarser layer goes on the bottom (gravel below, sand on top). Otherwise the sand sifts between the stones and both lose their function.
- Do I need to rinse aquasoil before planting?
- No. Aquasoil is baked granules — rinsing destroys their structure. Just pour it in and slowly add water through a bag or plate so you don't blow out the layer.
Goldie editorial team
Practising aquarists with a combined 30+ years of experience · Biologists and editors, fact-checking against FishBase and Seriously Fish · Every piece is reviewed by a qualified ichthyologist before publication
PhD in ichthyology, researcher of African Great Lakes cichlids
PhD in ichthyology, University of Edinburgh · Field research in Malawi, Tanganyika and Victoria (2013–2018) · 12+ peer-reviewed publications on cichlid behaviour
Sources
- Tropica Soil — Product page · Tropica · 2026-05-22
- ADA Aqua Soil Amazonia · ADA · 2026-05-22
- Practical Fishkeeping — Substrate guide · Practical Fishkeeping · 2026-05-22