Discus water parameters: a complete table of ideal values
The ideal water parameters for discus — a complete table with optimal values (29°C/84°F, pH 6.0–6.8, TDS 100–200 ppm, KH 2–5, GH 3–8) and acceptable limits for every metric.
Quick summary
- Temperature: 28–30°C (82–86°F), optimal 29°C (84°F) — the single most critical parameter.
- pH: 6.0–6.8 ideal (5.5–7.5 acceptable for farm-raised discus).
- TDS: 100–200 ppm for keeping, 50–150 ppm for breeding.
- KH: 2–5 dKH (at least 2 to avoid a pH crash). GH: 3–8 dGH.
- Ammonia (NH₃) and nitrite (NO₂): 0 ppm, always. Nitrate (NO₃): under 20 ppm.
- Stability matters more than the exact value — swings over 0.3 pH/day = stress.
In short
- Temperature: 28–30°C (82–86°F), optimal 29°C (84°F) — the most critical parameter.
- pH: 6.0–6.8 ideal (5.5–7.5 acceptable for farm-raised discus).
- TDS: 100–200 ppm for keeping, 50–150 ppm for breeding.
- KH: 2–5 dKH (at least 2 to avoid a pH crash). GH: 3–8 dGH.
- Ammonia (NH₃) and nitrite (NO₂): 0 ppm, always. Nitrate (NO₃): under 20 ppm.
- Stability matters more than the exact value — swings over 0.3 pH/day mean stress.
What you'll learn
Discus (Symphysodon spp.) are sensitive fish native to the soft, warm waters of the Amazon basin (Rio Negro, Rio Tefé, Rio Içá). This guide is the pillar for the Water Parameters category and gathers every key value into a single table, with links to specialized guides for each parameter. If you're just starting out, see the simple version: Discus water parameters for beginners (just 4 values).
The complete table — every value
| Parameter | Optimal | Acceptable | How to measure |
|---|---|---|---|
| 🌡️ Temperature | 29°C (84°F) | 27–32°C (81–90°F) | Digital thermometer |
| 🧪 pH | 6.0–6.8 | 5.5–7.5 | Liquid test (API, JBL, Sera) |
| 💧 TDS | 100–200 ppm | 50–400 ppm | Digital TDS meter |
| 🧂 GH (general hardness) | 3–8 dGH | 1–12 dGH | Liquid test |
| 🧪 KH (carbonate hardness) | 2–5 dKH | 1–6 dKH | Liquid test |
| ☠️ Ammonia (NH₃/NH₄) | 0 ppm | max 0.05 ppm | Liquid test |
| ☠️ Nitrite (NO₂) | 0 ppm | max 0.1 ppm | Liquid test |
| 🟡 Nitrate (NO₃) | under 10 ppm | max 40 ppm | Liquid test |
| 💨 Dissolved oxygen | over 6 mg/L | over 4 mg/L | O₂ test (optional) |
| 🟢 CO₂ (no injection) | 2–5 mg/L | under 15 mg/L | Drop checker |
💡 Hard water at pH 7.0–7.6 is acceptable for farm-raised discus (e.g. Stendker and other commercial strains). Only wild discus (Heckel, and Symphysodon from blackwater) genuinely need soft water (pH 5.0–6.0, TDS under 50).
The 3 golden rules
1. Stability beats the "perfect" value
A pH swing over ±0.3 units/day is stressful. Discus prefer water that's "imperfect but constant" over water that's "perfect but fluctuating."
2. Ammonia and nitrite = always 0
Any positive reading points to a biological filtration problem or overstocking. No healthy discus tolerates NH₃ over 0.05 ppm or NO₂ over 0.1 ppm over the medium term.
3. Stable pH = KH over 2 dKH
KH buffers the pH against sudden swings. Below 1 dKH, pH can fall under 5.0 overnight (a "pH crash") — which can be fatal for discus.
Why values drift
| Source of variation | Effect | Fix |
|---|---|---|
| Water change with cold water | Thermal shock, temp drop | Match the water temperature |
| Cleaning the filter with tap water | Kills bacteria → ammonia rises | Rinse media in tank water |
| Overfeeding | Decaying leftovers → NH₃, NO₂, NO₃ | 2 meals/day, remove leftovers |
| Dead plants | Ammonia release | Trim dead leaves weekly |
| CO₂ injected overnight | pH drops sharply | Solenoid on a timer |
| RO water with no KH | pH crash | KH at least 2 dKH (see KH & GH) |
How to test correctly — frequency
| Stage | What to test | Frequency |
|---|---|---|
| Cycling (4–6 weeks) | NH₃, NO₂, NO₃, pH | Daily |
| New tank (months 1–3) | All parameters | Every 2 days |
| Stable tank | NH₃, NO₂, NO₃, pH, T° | Weekly |
| KH, GH, TDS | After a major water change | Monthly |
| Problem (sick fish) | All + O₂ | Immediately |
🛒 A complete test kit such as the API Freshwater Master Test Kit (typically lasts 8–12 months) or the JBL ProAquaTest Lab covers everything. See How to test the water correctly.
Is your tap water suitable?
In most cases, yes — for farm-raised discus. What matters is checking your own supply, because tap water varies enormously by region.
| Check | Reading | Decision |
|---|---|---|
| Soft water | TDS under 250 ppm, pH 7.0–7.4 | ✅ Use directly + dechlorinator |
| Medium | TDS 250–350 ppm, pH 7.2–7.6 | 🟡 Optional 30% RO mix |
| Hard water | TDS over 400 ppm, pH over 7.5 | 🟡 Mix 40–60% RO |
| Very hard / limestone | TDS over 500 ppm | RO strongly recommended |
Always dechlorinate with a conditioner such as Seachem Prime, Tetra AquaSafe or JBL Biotopol — chloramine kills filter bacteria and damages fish gills. See Dechlorinating water for discus.
Detailed guides for each parameter
- The ideal pH for discus (6.0–6.8) — how to lower/raise it and keep it stable
- The ideal temperature (29°C / 84°F) — heating and Hexamita prevention
- TDS values (100–200 ppm) — control with RO and remineralization
- KH and GH (hardness) — avoiding a pH crash
- Ammonia and nitrite (0 ppm) — the emergency protocol
- Water changes — how often
- Mixing RO + tap water — a quick calculation
Final checklist — is your water OK?
- ☐ Temperature 28–30°C (82–86°F), stable to ±0.5°C
- ☐ pH between 6.0 and 7.5, no swings over 0.3/day
- ☐ TDS between 100 and 300 ppm (or under 400 with frequent changes)
- ☐ KH ≥ 2 dKH (anti pH crash)
- ☐ Ammonia = 0 ppm
- ☐ Nitrite = 0 ppm
- ☐ Nitrate under 20 ppm
- ☐ Water change 25–30% × 2/week with dechlorinated water
- ☐ Weekly test with a liquid kit (NOT strips)
- ☐ Filter cleaned only in tank water
What to do next
📚 Learn more:
🧮 Calculate:
- RO + tap water mixer — hit your target TDS
- Aquarium unit converter — TDS, °C/°F, °dGH
🛒 Buy:
- Verified breeders and trusted aquarium stores for professional water tests (API, JBL, Sera) and conditioners (Seachem Prime, JBL Biotopol).
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