Discus not eating: 7 causes and an hour-by-hour action plan

In short

• Normal: new discus may refuse food for 2–5 days after transport — don't panic.
• Common causes: acclimation stress • temperature under 28°C (82°F) • Hexamita • positive ammonia/nitrite • group bullying • sudden food change • early gill infection.
• First 24h plan: test the water (NH₃, NO₂, NO₃, pH, T°) → check temperature 29°C (84°F) → dim the lights → offer favorite food (frozen brine shrimp/bloodworms).
• 48–72h plan: if it refuses + other symptoms (white feces, fast breathing, darkening) → targeted treatment.
• Alarm: 7+ days without food or refusal + other symptoms = act immediately.
• Natural appetite booster #1: fresh crushed garlic on the food (3 cloves / 100g).

What you'll learn from this guide

Food refusal in discus (Symphysodon) is one of the first and most important clinical signals — healthy discus are always interested in food. But not every refusal is an emergency: a newly bought discus that refuses for 2–5 days is completely normal, while a discus from established stock that suddenly stops eating for 24h indicates a serious problem. This guide shows you 7 common causes, the hour-by-hour action plan (first 24h, 48–72h, after 1 week) and when to genuinely worry.

Normal vs alarming refusal

The 7 common causes

1. Transport / acclimation stress ⭐⭐⭐⭐⭐

The most common and completely normal.

• Duration: 2–5 days, sometimes up to 7 days
• Fish appearance: slightly pale / darkened colors, sits in a corner, swims hesitantly
• Action: Wait. Dim lights, quiet, stable parameters.

2. Temperature under 28°C (82°F) ⭐⭐⭐⭐⭐

Below 28°C (82°F) the discus metabolism slows dramatically.

• Check: a digital thermometer (not the stick-on type — inaccurate)
• Target: 29°C (84°F) stable
• Action: adjust the thermostat; if the heater is faulty → replace it

3. Hexamita (internal parasites) ⭐⭐⭐⭐⭐

The #1 cause of prolonged refusal with weight loss.

• Associated symptoms: long white feces, visible weight loss (a sharp spine), holes in the head (HITH)
• Action: Metronidazole 400 mg / 100L, 10 days — see the full Hexamita protocol

4. Positive ammonia / nitrite ⭐⭐⭐⭐⭐

Even 0.25 ppm ammonia = food refusal in discus.

• Check: a liquid test kit (NOT strips)
• Action: 50% water change + Seachem Prime double dose + check the filter

5. Group bullying ⭐⭐⭐⭐

Dominant discus can block access to food for the weaker ones.

• Signs: one discus always stays away, eats last, has bite marks on its fins
• Action: feed from 3–4 points at once, possibly rearrange the hardscape

6. Sudden food change ⭐⭐⭐

Discus are conservative with their diet.

• Action: gradual introduction over 7 days (75% old + 25% new → 50/50 → 25/75 → 100%)

7. Early gill infection ⭐⭐⭐

An affected gill = a weakened fish = food refusal.

• Associated symptoms: rapid breathing, gasping at the surface, a stuck operculum
• Action: eSHa 2000 + maximum aeration

The hour-by-hour action plan

First 24 hours — quick diagnosis

24–72 hours — targeted intervention

After 7 days — emergency

If the fish eats nothing at all for 7 days and there's no improvement:

• Isolate in a hospital tank
• Empirical treatment: Metronidazole + Levamisole combo (see the essential aquarist's pharmacy)
• Syringe force-feeding in extreme cases (specialists only)

Tricks to restart the appetite

✅ Fresh crushed garlic — 2–3 cloves / 100g of food, left for 5 min before feeding (an almost guaranteed effect)

✅ Live brine shrimp (hatched at home) — the movement triggers the hunting instinct

✅ Frozen bloodworms — visually attractive (red) and by smell

✅ A vitamin supplement (e.g. a liquid fish multivitamin) dripped directly onto the food — vitamins + a pleasant smell

✅ Food at the right temperature — beef heart thawed in warm tank water, NOT cold from the freezer

✅ Feeding in the morning after the lights come on (peak natural appetite)

✅ Reduce the light to 30% — more relaxed fish

Common mistakes

❌ Overfeeding when it isn't eating — the water turns toxic quickly, worsening the problem

❌ Switching between several food types at once — the discus shut down even more

❌ Adding medication preventively without a diagnosis — risk of making it worse

❌ Raising the temperature to 32°C (90°F) thinking it helps — correct only for Ich, dangerous for other diseases

❌ Stopping water changes "to avoid stress" — exactly the opposite of correct

❌ Force-feeding with a syringe without experience — risk of physical injury

Final checklist — discus refusing food

• ☐ Tested the water fully (NH₃, NO₂, NO₃, pH, T°)
• ☐ Checked the temperature 29°C (84°F)
• ☐ Checked the feces (normal / white / absent)
• ☐ Checked the breathing (normal / fast)
• ☐ Checked the colors (vivid / pale / darkened)
• ☐ Checked whether the whole group or just one
• ☐ Checked the recent history (transport, food change, interventions)
• ☐ Reduced lights by 50%
• ☐ Offered favorite food with garlic
• ☐ Decided: wait (normal) vs intervene (emergency)

What to do next

📚 Continue learning:

• Hexamita and HITH — the #1 cause of prolonged refusal
• Discus with white feces — a correlated symptom
• Bacterial gill infections — another cause of refusal
• The aquarist's pharmacy — a kit for treatments

🔧 Practical resources:

• Visual diagnosis — quick answers to symptoms
• Treatments — shop
• Premium food — shop

🐠 Final tip: Food refusal is just a symptom, not a disease — focus on finding the cause. With a good water test kit and careful observation, you'll identify the problem within 24–48 hours in 90% of cases. Don't panic in the first days with new discus, but don't ignore a stable discus that suddenly refuses — the difference between normal and emergency is, again, in the details.