Silver Arowana (Amazon)
Origin water: pH 5.5–6.5, very soft (GH 1–4), warm (78–84°F). Captive tolerance: pH 6.5–7.5, GH 4–10.
Most municipal tap water in tropical regions is suitable without adjustment. North American and European tap water often needs RO mixing to reduce hardness.
Asian Arowana (Southeast Asia)
Origin water: pH 6.0–7.0, soft (GH 2–6), warm (80–86°F). Captive tolerance: pH 6.5–7.5.
Asian arowanas thrive in slightly warmer water than silvers. Heater should hold 82°F minimum.
Black Arowana (Rio Negro)
Origin water: pH 4.5–6.0, extremely soft (GH 0–2), warm (78–84°F), heavily tannin-stained. Captive: keep pH under 7.0, soft as possible.
This is the most demanding species for water chemistry. RO water with mineral additions is often required outside the tropics.
Jardini Arowana (Australia)
Origin water: pH 6.5–7.5, moderate hardness (GH 5–12), warm (78–84°F). Captive tolerance: pH 6.8–8.0.
Jardinis tolerate harder water better than other arowana species. Most tap water works directly.
How to Soften Hard Tap Water
Reverse osmosis (RO) units produce near-pure water (0 TDS, 0 GH). Mix RO 50:50 or 70:30 with tap water to hit target hardness.
Indian almond leaves, peat moss, and driftwood release tannins that lower pH gradually and provide blackwater benefits.