Aquarium Substrate Guide: Gravel, Sand, and Soil Options UK

What Is the Gravel: The Versatile Standard?

Aquarium gravel is the most commonly used substrate in UK fishkeeping. Available in sizes from fine (2 mm) to coarse (5+ mm), natural or coloured, and rounded or angular, gravel suits the widest range of fish species and tank types. Standard natural gravel (pea gravel, river gravel) is inexpensive at 3-8 pounds for a 5 kg bag and is available from aquatic shops, garden centres, and online retailers.

For planted tanks, fine gravel (2-3 mm) works well with root-feeding plants when supplemented with root tab fertilisers. The gaps between gravel pieces allow water circulation around roots, promoting healthy growth. Epiphyte plants (Java Fern, Anubias) do not grow in substrate at all, so gravel is irrelevant for them. Coarse gravel (4-5 mm) traps more debris in the gaps, requiring more thorough gravel vacuuming during water changes.

Choose rounded gravel rather than angular or sharp-edged varieties, especially for tanks housing bottom-dwelling fish or species that sift substrate through their gills. Avoid painted or dyed gravel, as the coating can chip off over time, potentially releasing chemicals and creating a messy appearance. Natural gravel in brown, grey, or black tones provides the most natural look and makes fish colours pop. Our tank cleaning guide covers gravel vacuuming technique.

What Is the Sand: Natural and Fish-Friendly?

Sand substrates create a natural, smooth-bottomed appearance that closely resembles many natural fish habitats. They are the preferred substrate for bottom-dwelling fish species including Corydoras catfish (which sift sand through their gills to filter food), kuhli loaches (which burrow into soft substrates), and cichlids that dig and rearrange substrate. Sharp gravel can damage the sensitive barbels of Corydoras; fine sand eliminates this risk.

Play sand (available from UK builders’ merchants and Argos for 2-4 pounds per 15 kg) works well after thorough rinsing but compacts more easily. Aquarium-specific sand (such as Unipac or JBL Sansibar) is pre-washed and graded for consistent grain size at 5-10 pounds per 5 kg. Pool filter sand is another popular, affordable option with a coarser grain that compacts less. Avoid very fine sand (beach sand, silica sand) that compacts into an anaerobic layer and releases hydrogen sulphide gas.

The main maintenance consideration with sand is compaction. Over time, sand can form dense layers that prevent water circulation, leading to anaerobic pockets where toxic hydrogen sulphide gas develops. Prevent this by gently stirring the sand surface with a fork or stick during weekly water changes, keeping Malaysian Trumpet Snails (which burrow through sand and aerate it naturally), or choosing a coarser sand grade. Our maintenance schedule includes sand-specific care steps.

What Is the Aquarium Soil: The Planted Tank Choice?

Aquarium soils are nutrient-rich substrates specifically formulated for growing aquarium plants. Brands like Tropica Aquarium Soil, Fluval Stratum, JBL ProScape Volcano Mineral, and ADA Amazonia provide the nutrients, grain size, and cation exchange capacity that promote robust plant root growth. They are the substrate of choice for serious planted tanks, aquascapes, and anyone growing demanding plant species.

Aquarium soils typically lower pH and soften water, which benefits many tropical fish and plant species but may be unsuitable for fish requiring hard, alkaline water (African cichlids, livebearers). Expect some initial water cloudiness and ammonia release during the first 2-4 weeks with fresh soil, requiring frequent water changes before adding fish. This cycling period is well-established and temporary.

The cost of aquarium soil (typically 15-25 pounds for a 9-litre bag) is higher than gravel or sand, but for planted tanks, the improved plant growth often eliminates the need for root tab fertilisers, partially offsetting the cost. Soil substrates typically last 1-3 years before their nutrient content and buffering capacity deplete, at which point they can be supplemented with root tabs rather than replaced. Our tank setup guide covers substrate selection for different tank types.

What Are the Specialist and Mixed Substrates?

Many successful aquariums use mixed substrate approaches. A popular method is layering nutrient-rich soil beneath a cap of sand or fine gravel. The soil provides root nutrition while the cap prevents cloudiness and provides a clean aesthetic. Use at least 2-3 cm of capping material to prevent soil from surfacing during planting or fish activity.

Coral sand and crushed coral raise pH and hardness, making them suitable for African cichlid tanks, marine setups, and brackish aquariums. They are not appropriate for soft-water species or planted tanks (high pH inhibits nutrient absorption). Inert substrates like black quartz sand or silica gravel do not affect water chemistry, making them suitable for any species and any water chemistry requirement.

Specialised substrates include laterite (iron-rich clay placed under gravel for plant nutrition), peat substrate (lowers pH and tints water for blackwater biotopes), and volcanic rock granules (porous, lightweight, good for beneficial bacteria colonisation). These specialist options address specific requirements and are typically used in combination with standard substrates rather than alone. Our decoration guide covers combining substrates with hardscape for an attractive layout.

How Should You Choose the Right Substrate for Your Tank?

The best substrate choice depends on three factors: your fish species, your planting ambitions, and your aesthetic preference. For a standard community tank with beginner plants, fine natural gravel or sand works perfectly. For a dedicated planted tank or aquascape, aquarium soil provides the best growing conditions. For species-specific tanks (Corydoras, cichlids), choose the substrate that suits the fish’s natural behaviour.

Calculate the amount you need using this guideline: for a 3-5 cm depth, you need approximately 1 kg of substrate per litre of tank footprint (length x width in cm, divided by 1000, multiplied by the desired depth in cm). For example, a 60 x 30 cm tank base with 4 cm depth needs approximately 7-8 kg of gravel. Sand is denser than gravel, so you may need more by weight for the same depth. Aquarium soil is lighter, so less is needed.

Always rinse new substrate thoroughly before adding it to your tank. Place it in a bucket and run water through it until the water runs clear, stirring continuously. This removes dust, debris, and loose particles that would cloud your tank for days. Aquarium soils should be rinsed more gently (or not at all, per manufacturer instructions) to avoid breaking down the granules. Our tank cycling guide covers setting up substrate correctly before adding fish.