Aquarium Substrate: Sand, Gravel or Aqua Soil — What Should Go on the Bottom?
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.
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.
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.