A stable planted tank lives inside a band of healthy water parameters. None of these numbers is a magic target — plants and fish adapt to a wide range — but stability within a sensible band is what keeps growth strong and algae away. Here are the common ranges, what each does, and why a written record beats memory.
Open the tracker →| Parameter | Typical planted range | What it does |
|---|---|---|
| Temperature | 22–26 °C (72–79 °F) | Sets growth rate, oxygen and livestock comfort. |
| pH | 6.5–7.5 | Affects nutrient availability; with CO₂ it tracks carbon levels. |
| KH (carbonate hardness) | 3–8 dKH | Buffers pH and defines the CO₂/pH relationship. |
| GH (general hardness) | 4–12 dGH | Calcium & magnesium for plants, fish and shrimp. |
| NO₃ (nitrate) | 10–30 ppm | Main nitrogen source; too low stunts, too high feeds algae. |
| PO₄ (phosphate) | 1–3 ppm | Drives growth alongside nitrate. |
| Iron / trace | ~0.1–0.5 ppm | Lush green colour; shortage pales new growth. |
| Ammonia / Nitrite | 0 ppm | Must be zero in a cycled tank; anything else is toxic. |
Adjust to your stock and plants — soft-water species and shrimp prefer the lower hardness end, while many community fish are happy mid-range.
Fish and plants tolerate "wrong" numbers far better than they tolerate sudden swings. A tank sitting steadily at pH 7.4 is healthier than one bouncing between 6.8 and 7.6. The two biggest stability levers are consistent water changes and not chasing numbers with knee-jerk additives. Change one thing at a time and give it a week.
These three are linked. KH buffers pH, and injected CO₂ lowers pH predictably for a given KH. That's why a stable KH makes CO₂ dosing safe and readable — your pH drop becomes a reliable proxy for carbon. Let KH crash and your pH (and CO₂ readings) become erratic.
A single test tells you today's snapshot; a trend tells you the story. Logging your parameters with dates lets you see nitrate creeping up before algae appears, catch a KH that's slowly falling, or confirm that a new dosing routine actually moved iron into range. Range flags and history turn invisible drift into something you can act on early.