Ideal pH Range
Asian arowana (dragon fish) prefer 6.5-7.0 — slightly acidic. Silver arowana thrives at 6.0-7.0. Jardini and black at 6.5-7.5.
Any pH within range is fine if stable. Fluctuations of 0.3+ overnight cause more harm than being 0.2 above or below "ideal."
Lowering pH Naturally
Add driftwood (Malaysian or Mopani) — releases tannins that buffer pH down gently. Indian almond leaves have similar effect and add antibacterial compounds.
Avoid commercial pH-down chemicals. They shock the system and rebound within days.
Raising pH Naturally
Add crushed coral or aragonite substrate. Releases calcium carbonate slowly, raising pH toward 7.5-8.0.
Seashells, limestone, and Texas Holey Rock have the same effect. Remove once target is reached or it keeps climbing.
Buffer Capacity (KH)
KH under 4 dKH = unstable. Even a small waste load crashes pH. Target KH 5-10 dKH for stable arowana tank.
Raise KH with baking soda (1/4 tsp per 100L raises 1 dKH). Always test after dosing.