Water parameters sound intimidating, but understanding just a few of them is what separates thriving tanks from struggling ones. This guide explains pH, GH, and KH in plain language: what they are, why they matter, and what to actually do about them.
pH: How Acidic or Alkaline Your Water Is
pH measures acidity on a scale of 0–14, where 7 is neutral. Most freshwater fish do well between 6.5 and 7.5, though preferences vary by species.
What matters most is stability, not hitting a perfect number. A stable pH of 7.6 is far healthier than a pH that swings between 6.8 and 7.4. Sudden pH changes stress fish badly and can be fatal.
💡 Pro tip: Never chase a specific pH with chemical adjusters unless you really know what you're doing. They often cause unstable swings that are worse than the original wrong pH.
KH: Carbonate Hardness (Your pH Buffer)
KH measures the carbonates and bicarbonates in your water. Its real job is to act as a buffer that stops your pH from crashing.
- Low KH = unstable pH that can drop suddenly (dangerous)
- Adequate KH = stable, reliable pH
If your pH keeps falling over time, low KH is usually the cause. Most community tanks are happy with a KH of around 4–8 dKH.
GH: General Hardness (Minerals for Health)
GH measures dissolved minerals, mainly calcium and magnesium. Fish, shrimp, and snails need these minerals for healthy growth, and they affect which species will thrive in your water.
- Soft water (low GH): suits tetras, rasboras, and many South American species
- Hard water (high GH): suits livebearers (guppies, mollies), shrimp, and African cichlids
The easiest path to success is to choose fish that match your tap water rather than constantly altering your water chemistry.
How to Test (and How Often)
- Use a liquid test kit; test strips are too inaccurate for KH and GH
- Test your tap water first so you know your baseline
- Re-test whenever fish look stressed, after adding new décor, or if pH seems to drift
What to Do With Your Results
For most beginners, the best strategy is simple: test your tap water, pick fish suited to it, and keep parameters stable with regular partial water changes. Only adjust chemistry deliberately and slowly if you're keeping a species with specific needs.
Find liquid test kits and water care products in our Water Care range.
