Aquarium Substrate: Sand, Gravel or Aqua Soil — What Should Go on the Bottom?
Published by Planète Pets · managing editor: Clément Lacaille · how our guides are written
An aquarium's substrate isn't just a matter of aesthetics: it houses beneficial bacteria, feeds the plants and determines the comfort of bottom-dwelling species. Getting it wrong at the start means tearing everything down later. Here's how to make the right choice before the water goes in.
Contents · 5 sections
The three main substrate families
- Inert sand and gravel (quartz, river sand): neutral, they don't alter the water parameters. Easy to clean and cheap: 5 to 15 € per 10 kg bag. Perfect for a lightly planted tank or undemanding plants.
- Nutrient-rich soil under a sand cap: a fertile base layer (aquatic soil, 10 to 25 € per 5 litres) covered with 3 to 5 cm of gravel. The classic recipe for a long-lasting planted tank.
- Active soil (aquascaping type): granules that feed the plants and slightly lower pH and hardness. Very effective but pricier, 20 to 40 € per 9 litres, and needs replacing after a few years.
How deep, and how much?
Aim for 4 to 6 cm of total depth, more towards the back to create perspective. In practice, allow roughly 1 kg of gravel per litre divided by ten: about fifteen kilos for a 100-litre tank, adjusted to the slope you want. Rinse sand and gravel thoroughly in clean water before laying them, until the rinse water runs clear: you'll spare yourself days of cloudy water.
Matching the substrate to your fish
Corydoras and other bottom-sifting fish demand a fine, non-abrasive sand, or their barbels will get damaged. Goldfish turn the substrate over constantly: choose rounded, medium-grade gravel — too large to be swallowed — and firmly anchored plants. Grain size is genuinely part of habitat welfare, just as much as the tank's volume.
Mistakes to avoid
- Novelty coloured gravel with sharp edges, which injures bottom-dwelling species.
- Calcareous substrates (some marine sands) that push hardness up without you understanding why.
- Laying active soil and then endlessly rearranging it: it crumbles and clouds the water.
- Skipping the siphoning: during water changes, run the gravel vacuum over the substrate to remove waste — a key part of water maintenance.
Our recommendation
For a first planted tank, the safe bet remains the duo of nutrient-rich soil plus quartz gravel: 25 to 40 € for a 100-litre setup, planting that gets off to a good start and simple upkeep. Find our substrate and decor selections in the habitat and tank enrichment sections of Planète Pets.
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This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.
