pH & KH
KH contributes to buffering, so very low KH can make pH easier to shift.
Water chemistry
Understanding Water Parameters
Aquarium test results can look like a wall of numbers when you first start. The useful part is understanding what each number tells you, which changes are dangerous, and when the best response is simply to stop adjusting things and let the aquarium remain stable.
Start here
A test result only matters when you know what it means.
Different fish, shrimp and plants have different requirements, so there is no single perfect set of aquarium parameters. The goal is to provide water that suits the animals you keep and to keep those conditions reasonably stable.
Stability is important, but it is not an excuse for unsafe water.
A stable ammonia reading above zero is still a problem. Stability
matters most when people are tempted to constantly alter otherwise
acceptable pH, hardness or temperature readings.
Temperature
More than just “warm” or “cold”.
Temperature affects metabolism, oxygen demand, feeding and the general activity of aquatic animals. Choose a temperature range based on the species in the aquarium rather than setting every freshwater tank to the same number.
Sudden changes can be more stressful than small day-to-day variation. When doing water changes, avoid adding replacement water that is dramatically warmer or colder than the aquarium.
pH
pH tells you how acidic or alkaline the water is.
A pH of 7 is neutral. Values below 7 are acidic and values above 7 are alkaline. The pH scale is logarithmic, so a change of one whole pH unit is much larger than the numbers make it look.
Many commonly kept aquarium species tolerate a range of pH values. Problems often begin when aquarists repeatedly add chemicals to force the water towards a target number, causing the pH to swing back and forth.
Do not chase pH without understanding why it is changing.
If pH is unstable, investigate hardness, substrate, rocks,
driftwood, source water and other factors before repeatedly adding
pH-adjusting products.
GH
General hardness measures dissolved minerals.
GH mainly reflects dissolved calcium and magnesium in freshwater. These minerals are biologically important and can be especially relevant for shrimp, snails and other animals that rely on adequate mineral availability.
Water with a low GH is often described as soft, while water with a higher GH is described as hard. The correct range depends on the species being kept.
KH
Carbonate hardness helps resist sudden pH changes.
KH describes the water's carbonate and bicarbonate buffering capacity. In practical aquarium keeping, a higher KH generally means the water can resist changes in pH more strongly.
Very low KH water may experience larger pH shifts if acids build up. That does not mean every aquarium should have high KH; some species naturally prefer softer, less buffered water.
Ammonia
In an established aquarium, the target is zero.
Ammonia enters the aquarium through animal waste, decomposing food and other organic material. In a functioning biological filter, beneficial microorganisms process it as part of the nitrogen cycle.
Detectable ammonia in an established aquarium deserves attention. Possible causes include an uncycled tank, sudden overstocking, excessive feeding, a dead animal, damaged biological filtration or another source of decay.
Established aquarium target
0 ppm
Nitrite
Nitrite should also be zero.
During the nitrogen cycle, ammonia is converted into nitrite before nitrite is converted into nitrate. Nitrite is toxic to aquarium animals and should not remain detectable in a mature, properly functioning aquarium.
Established aquarium target
0 ppm
Nitrate
Nitrate is the part you normally manage rather than eliminate completely.
Nitrate is produced later in the nitrogen cycle and is generally less immediately toxic than ammonia or nitrite. It can accumulate over time and is commonly controlled through sensible stocking, feeding, plant growth and regular water changes.
There is no single nitrate number that applies perfectly to every freshwater aquarium. Sensitive livestock may benefit from lower levels, and the important point is to avoid allowing nitrate and general waste to accumulate unchecked.
How the numbers connect
Aquarium parameters do not exist independently.
GH & livestock
Mineral content can affect animals such as shrimp and snails, particularly around growth and moulting.
Temperature & oxygen
Warmer water generally holds less dissolved oxygen while many animals simultaneously become more metabolically active.
Waste & stocking
More animals and more food increase the amount of waste the biological filter and maintenance routine must handle.
Testing
Test with a reason, not just because you own a test kit.
Testing is especially useful during cycling, after adding livestock, when animals behave unusually, after a suspected filtration problem or whenever something in the aquarium has changed significantly.
Keep a simple record if you are troubleshooting. A sequence of results over several days is often more useful than one isolated reading.
- Follow the instructions for your particular test carefully.
- Check expiry dates and storage instructions.
- Rinse test equipment after use.
- Repeat a result if it looks completely unexpected.
- Compare aquarium water with your source water when useful.
Common mistakes
Numbers can cause problems when they are treated like a scoreboard.
- Trying to achieve an exact pH because a care sheet lists one number.
- Changing several parameters at once and then not knowing what caused the result.
- Ignoring ammonia or nitrite because the fish still appear normal.
- Assuming clear water automatically means good water quality.
- Making large corrections instead of understanding the source water first.
- Testing inconsistently and comparing results produced with different methods.
Keep reading