Fundamentals · 11 min read
Aquarium water parameters
What the test kit is actually telling you.
Ammonia, nitrite, nitrate, pH, GH, and KH in a freshwater tank — what to test, what numbers to want, and when to panic.
Photo: Christian Ang / Unsplash
A cycled tank is not a vibe. It is numbers. If you only buy one kit, buy liquid tests for ammonia, nitrite, and nitrate. Strips are fine for pH once you trust them. They are not fine for ammonia on a new tank.
The nitrogen numbers
| Test | Want | Panic |
|---|---|---|
| Ammonia | 0 ppm | Anything above 0 with fish in the tank |
| Nitrite | 0 ppm | Anything above 0 with fish in the tank |
| Nitrate | Usually 5–40 ppm | 0 forever (not cycled) or climbing past 40–80 without water changes |
Ammonia and nitrite burn gills. Nitrate is the leftover that water changes remove. A tank that “looks clean” can still have ammonia. That is why we cycle before livestock. Full walkthrough: cycling a fish tank.
pH, GH, KH
pH is acidity. Most community fish live in 6.5–7.8. Chasing a perfect 7.0 with chemicals is how you stress fish. Match the fish to your tap, or pick fish that match your tap. See profiles for ranges.
GH is general hardness (calcium and magnesium). Shrimp and livebearers like some of it. Soft-water tetras like less. If you have very soft rainwater, remineralize for shrimp.
KH is carbonate hardness — the buffer that stops pH from swinging. Low KH plus a lot of CO₂ is how planted tanks crash pH overnight. The CO₂ calculator uses KH and pH together.
Temperature
Tropical community: 74–78°F is the usual compromise. Bettas and rams want the high end. White clouds and goldfish want the low end, or no heater. Run compatibility if you are mixing.
Heat the room’s problem, not a fantasy delta. The heater calculator uses tank gallons and how cold the room actually gets.
What to test, how often
- New cycle: ammonia and nitrite every day or two until both stay at 0 and nitrate appears.
- Running community: nitrate weekly, plus ammonia if anything looks off.
- After a death or cloudy water: ammonia first. Then nitrite. Then you can talk about algae.
If the water is white, read cloudy aquarium water. If fish are at the surface, read gasping and test immediately.
Related
- Freshwater vs saltwater aquariums
Freshwater vs saltwater: cost, equipment, livestock, and why FishBaseHQ stays on the freshwater side of the glass.
- You are feeding too much
How much to feed freshwater fish, how often, and how leftover food shows up as cloudy water, algae, and nitrate spikes.
- How often should you change aquarium water?
How often to change aquarium water, how many gallons to pull, and how to dose conditioner on the new water only.