Aquarium water parameters
Every freshwater parameter, one page each — what it is, where it should sit, how to read it, what to do when it drifts.
Manfred · the reference shelf
One parameter at a time, in plain language. Ranges come straight from the same chemistry reefnotes uses to grade your tests, so the numbers on each page match the badges in the app.
Core parameters
- Ca
Calcium (Ca)
The dominant cation in general hardness. What shrimp build moults from, what snails build shells from, and a macronutrient most planted tanks have plenty of.
- CO2
Carbon dioxide (CO₂)
The single nutrient that decides whether a planted tank lights up or limps along. Calculated from pH and KH, dangerous when over-injected.
- Fe
Iron (Fe)
The micronutrient that decides whether your red plants are red. Tiny target band, fast turnover, easy to over-dose.
- GH
General hardness (GH)
The total calcium + magnesium concentration. The number that decides whether livebearers thrive or shrimp moult cleanly.
- K
Potassium (K)
The third macronutrient. The one no GH or KH test measures, the one a freshwater tank can run completely empty on, and the one most cheap fertilisers underdose.
- KH
Carbonate hardness (KH)
How much acid your water can absorb before pH crashes. The carbonate buffer that holds pH steady — and the one that lies about CO₂ when it's wrong.
- Mg
Magnesium (Mg)
The smaller half of general hardness, the centre atom of chlorophyll, and the parameter most planted-tank deficiencies actually trace back to.
- NH4
Ammonium / Ammonia (NH₄ / NH₃)
The first step of the nitrogen cycle and the acute fish-killer. Should read zero in any cycled tank.
- NO2
Nitrite (NO₂)
The toxic middle step of the nitrogen cycle. In an established tank it should always read zero.
- NO3
Nitrate (NO₃)
The end product of the nitrogen cycle. Plant fertiliser at the right level, fish stressor when it climbs.
- pH
pH
The acidity-alkalinity of the water on a log scale. Where it sits matters less than how steady it stays — and what it tells you about CO₂.
- PO4
Phosphate (PO₄)
A macronutrient for plants, a fuel for algae, and a parameter people keep misreading as bad-when-non-zero.
- SiO2
Silicate (SiO₂)
The nutrient diatoms grow on. Usually a tap-water inheritance, usually responsible for new-tank brown algae.
- Temp
Temperature
The parameter that drives metabolic rate for everything in the tank. Stable matters more than precise.
Trace elements
Micronutrients and toxicity ceilings — useful when a plant is sulking or a test kit shows up positive.
- B
Boron (B)
A trace micronutrient plants need at very low concentrations. Included in most complete trace mixes; rarely tested alone.
- Cu
Copper (Cu)
Acutely toxic to shrimp, snails, and many corals. A ceiling parameter — there's no "ideal" copper, only "below the threshold".
- Mn
Manganese (Mn)
A plant micronutrient that pairs with iron in most fertilisers. Rarely deficient alone, often the missing partner when iron dosing "isn't working".
- Mo
Molybdenum (Mo)
A trace nutrient plants need at near-homeopathic concentrations. Important for nitrogen metabolism; almost never deficient alone.
- Zn
Zinc (Zn)
A trace micronutrient plants need at low concentrations. Included in most complete trace mixes; toxic if substantially over-dosed.
These pages give you the model. reefnotes applies it — to your tanks, your tests, your cadence — in the background.