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 the first 2-6 weeks: must cycle the tank fishless before stocking, or use a heavy plant load to consume the NH3 as fertiliser
- Acidifies the water (pulls pH toward 6.0-6.5 and softens KH), which suits soft-water community fish and most plants but is incompatible with hard-water species
- Exhausts in 1-3 years depending on plant load; the granules eventually become inert and the tank shifts to a root-tab-dosed system
Premium aquasoils (ADA Amazonia, Tropica) are the planted-tank gold standard but expensive ($40-80 per 9L bag, two-three bags for a typical 60L tank). Budget alternatives (Fluval Stratum, Landen) work but with less nutrient density and shorter longevity. Do not stir vigorously once placed; granules crumble and turn to mud.
Bare bottom (no substrate)
Also known as: Bare bottom, Glass bottom
- Maximum visibility of detritus: anything that drops to the bottom is obvious and easy to siphon, making this 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 zones to worry about; no substrate to vacuum during water changes
- Some fish (cory cats, kuhli loaches, eels) dislike a bare bottom and become reclusive without a soft substrate to forage on
Standard practice in discus breeding tanks, shrimp colony setups, and quarantine tanks. Aesthetically divisive; works visually with planted hardscape (wood + epiphytes + moss) but feels clinical with just fish. Reflection from the tank floor can stress some species: a thin sand bed in a far corner or a mat of moss helps.
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 ("Ecology of the Planted Aquarium") is the canonical reference. Soil must be unfertilized, pesticide-free, mineralized through multiple wet-dry cycles before placement. Cap with at least 2.5 cm (1 inch) of inert sand or fine gravel. Not recommended for first-time planted tanks; 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 extensive water-column dosing to thrive
- Larger particles let mulm settle into the substrate; needs gravel vacuuming during water changes or anaerobic zones develop
- Vinegar test before stocking: if the gravel fizzes when wet vinegar is dropped on a few stones, it contains calcium carbonate and will raise pH/KH (treat it as limestone gravel instead)
- Compatible with most fish; only sand-sifters 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 lasts forever. Avoid pink/red gravel that may be limestone (use the vinegar test).
Inert sand
Also known as: Pool filter sand, Silica sand, Play sand (washed), Black diamond blasting sand
- Provides no nutrients to root feeders: heavy-feeding plants (swords, crypts) will yellow and stall without root tabs supplementing
- Cory catfish, kuhli loaches, and other substrate-sifters thrive on fine sand which lets them filter without scratching their barbels
- Anaerobic pockets form over time under uniform fine sand; periodic gentle stirring or malaysian trumpet snails prevent hydrogen sulfide buildup
- Easy to clean with a gravel vacuum held just above the surface; debris lifts off without pulling up the sand itself
Rinse aggressively before adding to the tank or expect cloudy water for hours. Pool filter sand is the cheapest reliable option in the US; "black diamond" sandblasting sand is industrial-grade but works fine in freshwater (rinse thoroughly). Avoid play sand without washing; the surfactants kill fish.
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: pure aragonite eventually dissolves down to less-soluble residue and stops affecting water chemistry. Replace or top up every few years. Mixing with inert sand (50/50) gives moderate buffering for soft-medium water targets.
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
Fluorite and Eco-Complete are the established products. Rinse Fluorite extensively before use (it leaves a dust cloud that takes weeks to settle if you skip this). Eco-Complete ships pre-rinsed. Both are heavier than gravel, which helps anchor large plants but adds shipping cost.
Wood and rock mounts
Also known as: Hardscape mount, Epiphyte mount, Driftwood attachment, Botanical mount
- Plant material attaches to driftwood or porous rock with thread, glue, or its own rhizome roots; substrate underneath is independent of the plants
- Hardwood driftwood releases tannins that stain water amber and lower pH slightly (the "blackwater" look); rock effects depend entirely on the stone (vinegar-test it)
- Required setup for the most popular low-tech aquarium plants: anubias of all sizes, java fern, bolbitis, all aquarium mosses, bucephalandra
- Plants do not draw from substrate: rely on water-column dosing for nutrients regardless of what is in the tank floor
Rhizome plants (anubias, java fern, bucephalandra) attached to wood or rock are the most common entry point to planted tanks because they tolerate almost any water and don't need a special substrate. Pair with any of the other substrates (or bare bottom) underneath, depending on what other plants and fish are in the tank.