Ideal Range
pH: 6.0-7.0 (slightly acidic to neutral).
GH: 4-8 dGH (soft to medium-soft).
KH: 3-6 dKH (low buffer to allow soft water).
Temperature: 75-80°F.
Why Soft Water?
Tetras evolved in Amazon and Orinoco basin waters with very low mineral content. Their kidneys, gill function, and reproductive systems are adapted for soft water.
In hard water (GH 12+), tetras suffer chronic stress. Lifespan drops, breeding fails, color fades.
- ✦Test your tap water — most municipal water is medium-hard.
- ✦Hard-water tetras (X-ray, lemon) tolerate harder water.
Softening Hard Water
RO water mixed with tap water is the cleanest approach. Mix 50/50 to halve hardness; mix 75/25 RO/tap for very soft water.
Indian almond leaves and driftwood release tannins that lower pH and slowly reduce hardness.
Peat moss in the filter softens water gradually but stains it brown.
Stability Matters Most
Stable parameters beat perfect parameters. Sudden swings (water changes with very different parameters) kill tetras within hours.
Pre-mix water in storage containers, age 24 hours, and match temperature to the tank before adding.
Hard-Water-Tolerant Tetras
Lemon tetras, x-ray tetras, black skirt tetras, glowlight tetras tolerate harder water (GH 12+) better than neons or rummy-nose.
If your tap water is very hard and you do not want to use RO, choose these species.