Water discussions can get confusing fast because people mix up pH, GH, and KH. For guppies, the simple truth is that they tend to do best in stable, mineral-rich water. Many Australian tap supplies are naturally suitable. The biggest problems usually come from very soft water with low buffering, or from chasing pH and causing swings. If you can read your tap tests properly, you’ll know whether you actually need to change anything.
What the numbers mean
- GH: general hardness (minerals like calcium/magnesium). Supports colour, fertility, and strong development.
- KH: carbonate hardness (buffer). Helps prevent pH swings.
- pH: acidity/alkalinity. Less important than stability, but influenced by KH.
When hard water is fine (or even ideal)
If GH and KH are moderate and stable, guppies usually thrive. Hard water becomes a “problem” mostly when extremes create scale, equipment issues, or you keep species that prefer soft water — not because guppies hate minerals.
When soft water causes issues
- pH swings between water changes
- poor fry survival or weak development
- fish that look stressed despite “clean” water
What to change (only if needed)
- Low KH: gentle buffering support can reduce swings.
- Extreme softness: remineralising can help guppies long-term.
- Don’t chase pH: avoid fast chemical adjustments.
The most “guppy-friendly” water is the water you can keep consistent. Once you know your GH/KH, you can choose a routine that keeps parameters steady — and guppies reward steadiness more than perfection.
