Aquarium Water Parameters Guide 2026
The 7 parameters every fish keeper must understand and control
pH — Acid/Alkaline Balance
The pH scale runs from 0 to 14. A value of 7.0 is neutral — values below 7 are acidic, values above 7 are alkaline. Most freshwater fish thrive in a narrow band, and even a small drift of 0.5 units can cause measurable stress.
Ideal pH by Fish Type
| Fish / Species | Ideal pH Range | Notes |
|---|---|---|
| Tropical Fish (general) | 6.5 – 7.5 | Widest tolerance, easiest to keep |
| Discus / Cardinal Tetra | 5.5 – 6.5 | Soft acidic; RO water recommended |
| African Cichlids | 7.8 – 8.5 | Hard alkaline; crushed coral substrate |
| Goldfish / Koi | 7.0 – 8.0 | Adaptable but prefer slightly alkaline |
| Betta | 6.5 – 7.5 | Tolerates 6.0–8.0 but 7.0 is ideal |
| Cherry Shrimp | 6.5 – 7.5 | Consistent pH matters more than exact value |
How to Adjust pH
- Peat moss in filter
- Driftwood (natural tannins)
- RO / reverse osmosis water
- Indian almond leaves
- Crushed coral in filter (use sparingly)
- Aragonite / limestone substrate
- Baking soda (emergency — precise dosing only)
Ammonia (NH3/NH4) — The Silent Killer
Ammonia is produced continuously in every fish tank from fish waste, uneaten food, dead plant matter, and decomposing organic material. It is the primary nitrogenous waste product of the nitrogen cycle and the first parameter to spike in new or uncycled tanks.
Toxicity Levels
| Level (ppm) | Effect on Fish | Action Required |
|---|---|---|
| 0.0 ppm | Safe — healthy cycled tank | None — maintain |
| 0.25 ppm | Chronic stress begins, immune suppression | Investigate source, partial water change |
| 0.5 ppm | Visible stress: gasping, loss of appetite | Immediate 30-50% water change |
| 1.0 ppm | Gill damage, rapid breathing, red streaks | Emergency water change + remove source |
| 2.0 ppm | Death within hours for most species | Emergency: 70% water change immediately |
Test Kit Comparison
- Highly accurate (±0.05 ppm)
- Detects sub-dangerous levels
- ~$8–12 USD, 130 tests
- Recommended for all keepers
- Quick but less accurate
- Often miss 0.25–0.5 ppm range
- Cheaper per kit, more per test
- OK for routine checks, not diagnosis
Nitrite (NO2) — Oxygen Thief
Nitrite is the second stage of the nitrogen cycle — Nitrosomonas bacteria convert ammonia into nitrite. In a fully cycled tank, Nitrobacter/Nitrospira bacteria then convert nitrite to the less-toxic nitrate almost instantly. Nitrite typically spikes during weeks 2–3 of a new tank cycle.
How Nitrite Kills Fish — Brown Blood Disease
Nitrite enters fish blood through the gills and binds to hemoglobin, converting it to methemoglobin — which cannot carry oxygen. Fish literally suffocate even in well-oxygenated water. Blood turns brown (visible in gill tissue). Fish gasp at the surface despite adequate aeration.
Emergency Treatment
- Immediate 50–70% water change with treated water
- Add aquarium salt: 1 teaspoon per 10 litres — chloride ions compete with nitrite uptake through gill cells
- Increase surface agitation (more oxygen)
- Remove uneaten food, vacuum substrate
- Do NOT add more fish until 0 ppm confirmed for 2 weeks
Nitrate (NO3) — The Long Game
Nitrate is the end product of the nitrogen cycle — far less toxic than ammonia or nitrite, but it accumulates continuously and causes chronic harm at high levels. Unlike ammonia and nitrite, there is no bacterial process that removes nitrate in a standard tank — water changes are the only reliable control method.
Target Levels
Consequences of High Nitrate
- Algae blooms — nitrate is a primary fertilizer for nuisance algae
- Chronic stress — reduces disease resistance, dulls color, suppresses breeding
- Invertebrate deaths — shrimp are the first to show elevated nitrate stress
- Fin rot susceptibility — weakened immune response
Temperature — Stability Over Perfection
Cambodia Seasonal Guide
| Season | Months | Room Temp | Aquarium Risk |
|---|---|---|---|
| Cold Season | Nov – Jan | 20–28°C nights | Watch cold nights — may need heater for tropicals |
| Hot Dry Season | Mar – May | 28–34°C+ | Critical — chiller or AC required for Discus / Crystal Shrimp |
| Rainy Season | Jun – Oct | 26–30°C | Most stable; natural evaporation cools tanks slightly |
GH + KH — Hardness & pH Stability
GH — General Hardness
GH measures dissolved calcium and magnesium ions. These minerals are critical for shrimp molting, fish bone development, and osmoregulation. Low GH causes failed molts ("molting disease") in shrimp. Measured in dGH or ppm (1 dGH = 17.9 ppm).
KH — Carbonate Hardness
KH measures carbonate and bicarbonate alkalinity — the tank's ability to resist pH swings. KH is the most important parameter for pH stability. KH below 3 dKH = pH crash risk. KH above 6 = very stable pH. Measured in dKH.
Target GH/KH by Fish/Shrimp Type
| Species | GH (dGH) | KH (dKH) | Notes |
|---|---|---|---|
| Discus / Cardinals / Tetras | 3–8 | 2–5 | Soft acidic; RO + remineralizer |
| Betta / Guppy / Molly | 6–12 | 4–8 | Adaptable; tap water often fine |
| African Cichlids | 15–25 | 10–18 | Hard alkaline; crushed coral/aragonite |
| Goldfish / Koi | 8–15 | 6–12 | Moderate hardness; stable pH critical |
| Neocaridina (Cherry Shrimp) | 6–10 | 2–5 | Most forgiving shrimp; tap water OK |
| Caridina (Crystal Shrimp) | 4–6 | 1–2 | Soft pure water; RO mandatory |
| Livebearers | 12–20 | 8–15 | Hard water natives; salt helps |
TDS — Total Dissolved Solids
TDS measures everything dissolved in your water — minerals, salts, organics, and waste. A cheap TDS meter ($2–5 USD) gives an instant reading but does not tell you what is dissolved. High TDS could mean beneficial minerals (good) or accumulated organics (bad) — always interpret TDS alongside other parameters.
Shrimp TDS Targets
TDS Interpretation Rule
If TDS is rising without adding minerals — it means organics (waste, food residue, medications) are accumulating. This requires a water change, not adjustments. TDS rising after adding remineralizer = normal and expected. TDS rising in an unchanged tank = clean it.
Quick Reference: Water Parameters by Species
| Fish / Species | pH | Temp °C | GH (dGH) | KH (dKH) | Nitrate Max |
|---|---|---|---|---|---|
| Betta | 6.5–7.5 | 24–28 | 4–10 | 3–6 | 40 ppm |
| Guppy | 6.8–7.8 | 22–28 | 8–14 | 4–8 | 40 ppm |
| Goldfish | 7.0–8.0 | 15–22 | 8–15 | 6–12 | 50 ppm |
| Discus | 5.5–6.5 | 28–30 | 3–8 | 1–4 | 20 ppm |
| Cardinal Tetra | 5.5–6.5 | 24–28 | 3–8 | 2–5 | 20 ppm |
| African Cichlid | 7.8–8.5 | 24–28 | 15–25 | 10–18 | 50 ppm |
| Cherry Shrimp | 6.5–7.5 | 20–26 | 6–10 | 2–5 | 20 ppm |
| Crystal Shrimp | 5.8–6.6 | 20–24 | 4–6 | 0–2 | 10 ppm |
| Koi | 7.0–8.0 | 15–25 | 8–15 | 6–12 | 50 ppm |
* Values represent optimal ranges. Always research specific species requirements before purchase.
How to Test Your Water
API Master Test Kit
The industry standard for freshwater testing. Tests: pH, ammonia, nitrite, nitrate (high range pH too). Liquid reagents are far more accurate than strips.
- Fill test tube to 5ml line
- Add reagent drops as directed
- Cap, invert 5× to mix
- Wait stated time (varies by test)
- Compare to color card in good light
Digital Meters
- pH meter — calibrate monthly with buffer solution
- TDS meter — cheapest at $2–5, instant reading
- Thermometer — digital stick-on or probe
Digital meters are faster for daily monitoring. Liquid kits are more accurate for diagnosis. Use both.
Test Frequency Guide
- New tank: test daily until all zeros
- After new fish: test every 2–3 days for 2 weeks
- Established tank: weekly ammonia/nitrate check
- Shrimp tanks: TDS daily, full test weekly
- Before water change: quick TDS check
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