Every mystery death, algae bloom and "my fish look stressed" post comes back to the same six numbers. Learn what they mean, test weekly, and aquarium keeping stops being guesswork. Here's the working guide we give customers at our Sydney store.
The six numbers that run your tank
| Parameter | Target | What it tells you |
|---|---|---|
| Ammonia | 0 ppm, always | Waste being produced faster than bacteria convert it — toxic at any reading |
| Nitrite | 0 ppm, always | Cycle incomplete or crashed — as dangerous as ammonia |
| Nitrate | < 20–40 ppm | End product of the cycle — removed by water changes and plants |
| pH | 6.5–7.8 (stable) | Acidity — a steady "okay" beats a swinging "perfect" |
| GH / KH | Species-dependent | Minerals for healthy bones, shells and moults · KH buffers pH swings |
| Temperature | Steady, species range | Swings stress livestock more than being 1°C "off" |
The nitrogen cycle in 60 seconds
Fish waste → ammonia → bacteria convert it to nitrite → more bacteria convert that to nitrate → you remove nitrate with water changes and plants. Those bacteria live in your filter and substrate — which is why a new tank needs 4–6 weeks to "cycle" and why you never wash filter media in tap water (chlorine kills the colony).
Your weekly routine (10 minutes)
- Test the six numbers — liquid test kits beat strips for accuracy
- Change 10–15% of water, dechlorinated and temperature-matched
- Vacuum a different patch of substrate each week, never all at once
- Rinse filter sponge in the removed tank water when flow drops
The payoff: livestock this vibrant only happens in properly managed water.
When a number is off
- Ammonia/nitrite above zero: immediate 30–50% water change, feed less, test daily until zero. Livestock gasping = emergency.
- Nitrate creeping up: larger weekly changes, add fast-growing live plants — they eat nitrate for breakfast.
- pH drifting: usually exhausted KH — check GH/KH and remineralise with supplements rather than chasing pH chemicals.
- Cloudy or green water: separate issue — see how to get crystal clear water.
Species notes
Shrimp are the canary in the coal mine — they react to problems days before fish do (guide: why are my shrimp dying?). Snails need GH for shell health. Most community fish are flexible if changes are gradual — details per species in our water change guide.
Set your tank up to win
Good water is mostly good habits plus the right gear: minerals and conditioners, live plants, and livestock from healthy stock — everything ships with our Live Arrival Guarantee.
