Aquarium chemistry

• Nitrogen cycle

  NH₃/NH₄ → NO₂ → NO₃: 3–4 week cycling before fish; test nitrites 0, nitrates <20–40 mg/L.

• pH & hardness

  Most tropicals: pH 6.5–7.5, GH 5–15; stability beats the 'perfect' number.

• Water changes

  20–30% weekly with conditioner; a change is the only way to export nitrates without plants.

• Chemistry

  Dechlorinator is mandatory; salt/meds — only as needed, not 'for prevention'.

90% of 'sick fish' is water chemistry: nitrites >0 kill even a strong fish. Before buying fish — test NO₂ and NO₃, not 'how the water looks'.