What Is Blackwater
Blackwater habitats — Rio Negro tributaries, Borneo peat swamps, African forest streams — have water stained brown by tannins from decomposing leaves and wood. The water is soft, acidic (pH 4.5–6.5), and warm.
Blackwater fish: cardinal tetras, neon tetras, discus, angelfish, apistogrammas, chocolate gouramis, betta macrostoma, dwarf cichlids.
Tank Setup
Tank size: 20-gallon long minimum. Larger is easier to maintain.
Substrate: sand. Some keepers use aqua soil for additional pH-lowering effect.
Hardscape: driftwood (any species), branches, leaf litter.
Lighting: dim — 30 PAR maximum. Stronger light penetrates the tannins and looks unnatural.
Botanicals
Indian almond leaves (Catappa): the foundation. Add 1 leaf per 5 gallons. Replace as they decompose.
Alder cones: small cones rich in tannins. 5–10 per 10 gallons.
Mopani driftwood: continuously releases tannins for years.
Banana leaves, magnolia leaves, oak leaves: cheap leaf litter alternatives.
Cholla wood: hollow tubes, perfect shrimp shelter.
Water Chemistry
Tannins lower pH gradually. Starting pH 7.5 + heavy botanicals over 4 weeks → final pH 6.0–6.5.
For extreme blackwater (pH 5.0–5.5): use RO water + botanicals. Tap water has too much KH to drop below pH 6.0.
GH and KH drop over time. Test monthly and add minerals if needed for shrimp.
Maintenance
Water changes: 20% every 2 weeks. Use prepared water (RO + botanicals soaked for 24 hours) to maintain tannins.
Replace 25% of leaves and botanicals monthly.
No vacuuming the leaf litter — it's the ecosystem.
Plants for Blackwater
Most plants struggle in true blackwater (low light + low minerals).
Tolerant species: Cryptocoryne (especially crypt parva, balansae, retrospiralis), java fern, anubias, mosses, Bucephalandra.
Avoid: stem plants, vallisneria, Amazon swords (high mineral need).