How each substrate affects the system
Aquasoil
Also known as: ADA Amazonia, Tropica Aquarium Soil, Fluval Stratum, Landen Aquasoil, Brightwell FlorinVolcanit
- Pre-loaded with nitrogen, phosphorus, potassium, iron and trace elements: planted-tank specialists use it for rapid plant establishment without water-column dosing for the first 6-12 months
- Releases ammonia for roughly the first 2-6 weeks (ADA Amazonia can spike to around 2 ppm), so the tank must be cycled fishless before stocking, or carry a heavy plant load to consume the ammonia as fertiliser
- Acidifies the water, pulling pH toward about 6.0-6.5 and softening KH, which suits soft-water community fish and most plants but is incompatible with hard-water species
- Exhausts in about 1-3 years depending on plant load, after which the granules become inert and the tank shifts to root-tab dosing
Premium aquasoils (ADA Amazonia, Tropica) are the planted-tank standard but expensive, and budget alternatives (Fluval Stratum, Landen) work with less nutrient density and shorter life. Do not stir them vigorously once placed, since the granules crumble into mud. Because fresh aquasoil leaches ammonia, which is highly toxic to fish, the tank should be fishless-cycled or heavily planted before any fish are added.
Bare bottom (no substrate)
Also known as: Bare bottom, Glass bottom
- Maximum visibility of detritus: anything that drops to the glass is obvious and easy to siphon, which makes it the choice for breeders, shrimp colonies and species that benefit from extreme cleanliness (discus, fry-raising tanks)
- Forces plant choice toward epiphytes (anubias, java fern, mosses) mounted on hardscape, or floating plants
- No anaerobic substrate zones to manage and nothing to vacuum during water changes
- Bottom-foraging fish such as Corydoras catfish prefer a soft sand bed to root through with their barbels and tend to become reclusive or stressed on bare glass
Standard practice in discus breeding tanks, shrimp colony setups and quarantine tanks; breeding-tank guides commonly specify a bare bottom for hygiene. It is aesthetically divisive, working well with planted hardscape (wood, epiphytes and moss) but feeling clinical with fish alone, and floor reflection can stress some species, so a thin sand patch or a moss mat helps. Bottom-dwellers like Corydoras genuinely prefer a soft substrate to forage in.
Dirted tank (mineralized topsoil)
Also known as: DIY soil substrate, MTS, Walstad method substrate
- Cheapest possible nutrient-rich substrate: organic potting soil mineralized (dried, wetted, dried again, repeated) for several cycles, then capped with sand or gravel to prevent mud clouds
- Releases ammonia for the first 4-8 weeks like aquasoil; needs the same fishless cycling or heavy plant load
- Long-term nutrient supply: lasts 3-5 years before depletion, longer than aquasoil
- Caps must remain intact: if fish or maintenance disturbs the cap and soil mixes into the water column, the tank becomes a brown mess that takes weeks to settle
Diana Walstad's method, from 'Ecology of the Planted Aquarium', is the canonical reference; it uses soil in place of gravel, little or no added CO2 and filtration, modest lighting and a light fish load. The soil must be unfertilized and pesticide-free, mineralized through several wet-dry cycles before placement, and capped with at least 2.5 cm of inert sand or fine gravel. It is not recommended for a first planted tank, since aquasoil is more forgiving.
Inert gravel
Also known as: Aquarium gravel, Quartz gravel, Pea gravel (smooth)
- No nutrient capacity: stem plants and root feeders need root tabs or steady water-column dosing to thrive
- Larger particles let mulm settle into the substrate, so it needs gravel vacuuming during water changes or anaerobic pockets develop
- Vinegar test before stocking: gravel that fizzes when vinegar is dropped on it contains calcium carbonate and will raise pH and KH (treat it as limestone gravel instead), while quartz/silica gravel is inert
- Compatible with most fish; only sand-sifting species dislike the larger particles
Generic dyed aquarium gravel from pet stores works, but the coating can flake over years. Untreated quartz gravel from landscape suppliers is cheaper and effectively lasts forever, since quartz (silicon dioxide) is chemically inert. Avoid pink or red gravel that may be limestone, using the vinegar acid test to check.
Inert sand
Also known as: Pool filter sand, Silica sand, Play sand (washed), Black diamond blasting sand
- Provides no nutrients to root feeders, so heavy-feeding plants (swords, crypts) yellow and stall without root tabs
- Corydoras catfish, kuhli loaches and other substrate-sifters do well on fine sand, which lets them forage and sift without risking their barbels on sharp grit
- Uniform fine sand can develop anaerobic pockets over time; gentle periodic stirring or Malaysian trumpet snails prevent hydrogen sulfide buildup
- Easy to clean by holding a gravel vacuum just above the surface, so debris lifts off without pulling up the sand
Rinse it aggressively before adding it to the tank, or expect cloudy water for hours. Pool filter sand is the cheapest reliable option in the US, and 'black diamond' sandblasting sand is industrial grade but works in freshwater after thorough rinsing. Wash play sand especially well to remove fine silt and dust before use. Most of these are silica (quartz) sand, which is chemically inert.
Limestone gravel
Also known as: Crushed coral, Coral sand, Aragonite, Cichlid sand
- Continuously dissolves trace calcium carbonate, buffering pH upward (typically toward 7.8-8.4) and raising KH/GH
- Required for African Rift Valley cichlids (Mbuna, Tropheus) and many livebearers that need hard alkaline water
- Incompatible with soft-water species (tetras, discus, most South American cichlids) and acid-loving plants (most aquarium plants underperform above pH 7.8)
- Plant selection narrows considerably: only the hardiest plants (anubias, java fern, vallisneria, hornwort) tolerate the hardness
Buffering capacity is finite: aragonite slowly dissolves down to a less-soluble residue and eventually stops affecting water chemistry, so replace or top it up every few years. Mixing it 50/50 with inert sand gives moderate buffering for soft-to-medium water targets. Crushed coral, coral sand and aragonite are the same calcium carbonate chemistry.
Mineralized clay substrate
Also known as: Seachem Fluorite, CaribSea Eco-Complete, Iron-rich clay
- Iron and trace minerals are bound in the clay matrix, releasing slowly to plant roots over years; not a one-shot nutrient dump like aquasoil
- No water-chemistry shift: pH and hardness stay where they were, making it compatible with any fish species
- Lower starter nutrient density than aquasoil; pair with root tabs for heavy feeders and column dosing for stem plants
- Effectively permanent: the clay matrix does not break down and continues to host bacterial colonies and bind nutrients indefinitely
Seachem Fluorite and CaribSea Eco-Complete are the established products. Rinse Fluorite extensively before use, since unrinsed it leaves a dust cloud that takes weeks to settle, while Eco-Complete ships pre-rinsed. Both are heavier than plain gravel, which helps anchor large plants but adds shipping cost. They are porous clay-based gravels that hold iron and trace minerals without shifting water chemistry, so they suit any fish species.
Wood and rock mounts
Also known as: Hardscape mount, Epiphyte mount, Driftwood attachment, Botanical mount
- Epiphyte plants attach to driftwood or porous rock with thread, glue or their own rhizome roots, with the rhizome left exposed; the substrate underneath is independent of the plants
- Hardwood driftwood releases tannins that stain the water amber and lower pH slightly (the 'blackwater' look), while rock effects depend entirely on the stone, so vinegar-test it
- This is the standard setup for the most popular low-tech aquarium plants: anubias of all sizes, java fern, bolbitis, aquarium mosses and bucephalandra, whose rhizomes rot if buried
- The plants do not draw from the substrate, relying instead on water-column dosing for nutrients
Rhizome plants such as anubias, java fern and bucephalandra attached to wood or rock are the most common entry point to planted tanks, because they tolerate almost any water and need no special substrate; crucially their rhizomes must stay above the substrate, since burying them causes rot. Pair the mount with any other substrate, or a bare bottom, depending on the other plants and fish.