Ammonia and nitrite for discus: 0 ppm required (emergency protocol)

In short

• Ammonia (NH₃): 0 ppm REQUIRED — can be lethal from 0.5 ppm.
• Nitrite (NO₂): 0 ppm REQUIRED — lethal from around 1 ppm.
• NH₃ becomes far more toxic at pH above 7.
• Emergency protocol: 50% water change + a double dose of Seachem Prime + stop feeding for 24–48h.
• Common causes: uncycled tank, overstocking, overfeeding, cleaning the filter in tap water.
• Symptoms: red gills, gasping at the surface, lethargic fish, excess mucus.

What you'll learn

Ammonia and nitrite are the most dangerous toxins in an aquarium and the leading cause of death in new discus. They come from waste, decaying food and dead fish, and are converted (in order) NH₃ → NO₂ → NO₃ by the bacteria in your biological filter. This guide gives you the minute-by-minute emergency protocol, the common causes, and how to prevent a recurrence.

Critical values — what each level means

Why NH₃ becomes more toxic at higher pH

Ammonia exists in two forms:

• NH₄⁺ (ammonium) — relatively non-toxic, dominant at pH below 7
• NH₃ (free ammonia) — highly toxic, dominant at pH above 7

⚠️ 0.5 ppm total NH₃ at pH 7.5 is more dangerous than 1 ppm at pH 6.5. Discus in alkaline tap water are far more vulnerable.

Common causes

Symptoms in the fish — in order of appearance

1. Fish at the surface, gasping (low O₂ + gill burns)
2. Bright red gills or excess mucus on the gills
3. Food refusal (loss of appetite from toxicity)
4. Lethargy, sitting on the bottom or hiding
5. Pale / darkened colors (acute stress)
6. Erratic swimming, twitching
7. Hemorrhagic marks on the body/gills
8. Death — usually within 24–72h if untreated

Emergency protocol — minute by minute

Step 1 (first 5 minutes)

• ✅ Test NH₃ + NO₂ + pH with a liquid test (NOT strips)
• ✅ Prepare dechlorinated water at the same temperature (29°C / 84°F)
• ✅ Turn on extra aeration (oxygenation)

Step 2 (5–30 minutes)

• ✅ 50% water change, slowly (10 min to drain + 10 min to refill)
• ✅ Add a double dose of Seachem Prime (5 ml / 100 L) — temporarily neutralizes NH₃ + NO₂ for 24–48h
• ✅ Do NOT feed the fish

Step 3 (after 2 hours)

• ✅ Re-test NH₃ + NO₂
• ✅ If still >0.25 ppm → a second 30% change
• ✅ Monitor the fish's symptoms

Step 4 (days 1–7)

• ✅ Daily NH₃ + NO₂ test
• ✅ Double-dose Prime daily until readings are 0 ppm
• ✅ 25% water change daily for the first 3 days
• ✅ Resume feeding once a day, small amount, after 48h
• ✅ Identify and remove the cause (filter, stocking, feeding)

How to prevent a recurrence

A strong biological filter

• External filter, at least 5–6× tank volume per hour
• Bio media (bioballs, ceramic) at double the minimum amount
• Clean the filter only monthly, in water removed from the tank

Correct stocking

• Adult discus: 30–50 L (~8–13 US gal) of water per fish
• Juveniles: 15–25 L (~4–7 US gal) per fish
• Check ammonia every time you add new fish (after 48h)

Reasonable feeding

• 2 meals/day, amounts eaten within 2–3 minutes
• Remove leftovers right after feeding
• One fast day per week (recommended for adults)

A biological backup

Always keep on hand:

• Seachem Prime — an emergency neutralizer
• Seachem Stability — bacteria for filter recovery
• 2 mature filter sponges as a reserve

Common emergency mistakes

❌ 100% water change → you destroy the bacteria, NH₃ comes back worse ❌ Change water at a different temperature → thermal shock = double stress ❌ Cleaning the filter mid-emergency → extra stress ❌ Moving the fish to another tank → stress + you don't fix the cause ❌ Preventive antibiotic treatment → you kill the filter bacteria ❌ "It'll settle on its own" → no intervention = dead fish

Testing correctly with a liquid kit

API Freshwater Master or JBL Test are essential. Strips can be off by ±30% — at 0.5 ppm vs 1 ppm that's the difference between stress and death.

• Take the sample 5–10 cm (~2–4 in) below the surface (not from the surface)
• Shake the reagent bottle well first
• Read under white light (NOT a yellow bulb)
• Repeat if the value looks abnormal

Weekly prevention checklist

• ☐ Test NH₃ + NO₂ + NO₃ weekly
• ☐ Ammonia = 0 ppm
• ☐ Nitrite = 0 ppm
• ☐ Nitrate under 20 ppm (a sign of enough water changes)
• ☐ Filter clean (normal flow), cleaned monthly in tank water
• ☐ Stocking respected (30–50 L / ~8–13 US gal per adult)
• ☐ Moderate feeding, no visible leftovers
• ☐ Seachem Prime + Stability available at home

What to do next

📚 Learn more:

• Ideal water parameters
• How to test the water correctly
• The ideal pH for discus
• Cycling the aquarium

🛒 Buy:

• Verified breeders and trusted stores for Seachem Prime, Stability and API/JBL test kits.