measurement
Water testing
Test results are only as good as the method. Liquid reagent kits are substantially more reliable than strips for ammonia, nitrite and nitrate; strips are convenient for a quick KH and GH check. All reagents expire, and an old kit produces confidently wrong numbers.
In one sentence
Testing tells you what is happening in the water before the fish do. The essential set for a freshwater tank is ammonia, nitrite, nitrate, pH, KH and GH.
What to test and when
| Parameter | New tank | Established tank | Why |
|---|---|---|---|
| Ammonia | Every 1–2 days | When something looks wrong | Acute toxicity |
| Nitrite | Every 1–2 days | When something looks wrong | Acute toxicity |
| Nitrate | Weekly | Before each water change | Tracks maintenance |
| pH | Weekly | Monthly, and when investigating | Stability, and ammonia toxicity |
| KH | Weekly | Monthly | Early warning of a pH crash |
| GH | At setup | When stocking changes | Species suitability, invertebrate moulting |
Common testing errors
- Not shaking the second nitrate reagent hard enough or long enough, which reads far too low.
- Reading colours under artificial or coloured light rather than daylight.
- Using expired reagents. Write the opening date on the bottle.
- Testing tap water straight from the tap — dissolved CO₂ makes the pH read low until it has stood for 24 hours.
- Treating a single reading as a verdict. A trend across several readings is far more informative.