🪨 Substrates + gravel
Substrate isn't decoration — it's a biological filter, a plant nutrient bed, and (in some species) the difference between a stressed fish and a relaxed one. Cory catfish on coarse gravel = damaged barbels. Cichlids on fine sand = digging heaven. Here's how to match substrate to your stocking + plants.
Nutrient-rich baked-clay granules. ADA Aquasoil, Tropica Aquarium Soil, Fluval Stratum. Releases nitrogen + minerals to root-feeding plants. Lifespan 1–3 years before nutrients deplete + needs root tabs. Usually capped under nothing — sits on tank bottom.
Pool filter sand, play sand (rinsed thoroughly), or aquarium-branded sand. Cheap, looks natural, perfect for sand-sifters (cories, kuhli loaches, cichlids). Slightly trickier — fine grain can compact + create anaerobic pockets if not stirred occasionally.
The classic. Easy to clean (gravel vac), good water flow through it, suitable for fish-only + low-tech planted (with root tabs). Cheap. Pet-shop colourful gravels are often coated — fine for fish but check coating with a vinegar drop test if planting.
Same as inert sand/gravel but black — makes fish colours pop, plants look vibrant. CaribSea Tahitian Moon, Seachem Onyx. Slightly more expensive. No biological difference, just aesthetics.
No substrate. Used for: hospital tanks, breeding tanks, heavy-waste fish (large discus, plecos), African cichlids that endlessly redig. Easiest to clean. Looks clinical — hide with stones + caves if aesthetics matter.
Planted tanks: 5–8 cm of substrate so roots can spread (deeper at the back, shallow at front for visual depth). Fish-only: 2–3 cm enough — easier to vac clean. Avoid deep sand without occasional stirring (anaerobic pockets release toxic gases).
Cory catfish, kuhli loaches, eels: SAND only (coarse gravel damages sensitive barbels + scales). Plecos + cichlids: gravel or sand both fine, no sharp gravel. Goldfish: gravel large enough not to be swallowed (over 5 mm) or bare. Stingrays: very fine sand, no sharp edges.
New substrate ALWAYS comes dusty. Rinse in batches in a bucket with running tap water until water runs clear (10–30 minutes). Skip rinsing = murky tank for 2 weeks. Aquasoil exception — DO NOT rinse, it dissolves nutrients (just slowly fill tank with plate to break the flow).
Layer: 2–3 cm aquasoil OR potting-soil (no fertiliser added) → 3–5 cm inert sand or gravel CAP on top. Cap prevents soil floating + nutrient leech. Lasts years. Cheaper alternative to all-aquasoil setup. Walstad-style "dirted" tanks use this approach.
Some "natural" gravels are limestone — they raise pH + hardness. Drop vinegar on a sample: fizzes = limestone, avoid for soft-water species (tetras, discus, shrimp). Doesn't fizz = inert, safe for any species.
Gravel: siphon vac weekly during water change — pulls debris from inside the gravel. Sand: hover the siphon 1 cm above sand, sucks debris off the surface without removing sand. Bare-bottom: just siphon the floor, simplest of all.
Our substrates and gravel range goes live as we vet suppliers — we won't list anything we wouldn't use ourselves. In the meantime, our calculators, breed guides and AI vet tools below are free and don't need stock.
Depends on stocking. Sand is mandatory for cory catfish, kuhli loaches, eels (sensitive barbels). Gravel is easier to clean + better water flow for fish-only tanks. Most planted tanks use aquasoil capped with sand or gravel for both nutrients + aesthetics.
Yes — except for aquasoils (which dissolve if rinsed). All inert gravel + sand: rinse in a bucket with tap water until water runs clear. Skipping it = cloudy tank for 1–2 weeks + dust covering plants. Aquasoils: don't rinse, just fill tank slowly with a plate-on-substrate trick.
Planted tanks: 5–8 cm minimum (deeper at back for visual depth). Fish-only: 2–3 cm is plenty. Bare-bottom is fine for breeding/hospital tanks. Avoid super-deep sand layers without stirring — anaerobic pockets can release hydrogen sulphide.
It's possible but disruptive. Better: do it during a major rescape. Keep fish in a holding bin with tank water + filter media. Drain tank to substrate level, swap substrate (be patient with the dust), refill, restore filter, acclimatise fish back. Big project — plan a half-day at minimum.
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