What Happened To Your Fish?
White spots, torn fins, unusual swimming, rapid breathing, hiding, or appetite loss are often signs that something inside the aquarium may be changing. Match the symptom below to understand what to check first and what may be causing the problem.
Match What You’re Seeing
Select a visible symptom below to continue troubleshooting.
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Understanding The Full System
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Fish Illness Diagnosis & Actions
Match symptoms, understand possible causes, and review treatment direction.
Oxygen Stress
Common
Surface Gasping
Fish repeatedly staying near the surface struggling to breathe.
Oxygen Stress
Common
Surface Gasping
Fish repeatedly staying near the surface struggling to breathe.
Identification
What It Is
| Common Names | Surface Gasping, Oxygen Stress, Breathing Distress |
| Spread Risk | Not contagious |
| Main Cause | Low oxygen or unstable water conditions |
What You May See
| Behavior | Body Signs |
|---|---|
| Staying near surface | Rapid gill movement |
| Weak swimming | Clamped fins |
| Hiding or inactivity | Pale stressed coloration |
| Loss of appetite | Heavy breathing |
What To Check First
| Tank | Water | Recent Changes |
|---|---|---|
| Weak flow or aeration | Ammonia or nitrite spike | Added many fish recently |
| Filter stopped or clogged | Cloudy or foul-smelling water | Heavy feeding |
| Overcrowding | High temperature | Large cleaning or rescape |
Action Plan
What To Do Now
| Time | Action |
|---|---|
| Immediately | Increase surface movement and aeration |
| Immediately | Perform partial water change |
| Immediately | Stop feeding temporarily |
| Next 24 Hours | Monitor breathing and swimming behavior |
Important Warnings
- Do not overdose medication without confirming disease.
- Low oxygen can kill fish very quickly.
- High temperatures reduce oxygen availability.
- Dirty filters may reduce circulation and oxygen exchange.
- Surface gasping may also indicate ammonia or nitrite poisoning.
Recommended Product Direction
Breathing Stress
Water Related
Gill Disease
Red swollen gills with rapid breathing and oxygen distress.
Breathing Stress
Water Related
Gill Disease
Red swollen gills with rapid breathing and oxygen distress.
Identification
What It Is
| Common Names | Gill Disease, Gill Irritation, Gill Damage |
| Spread Risk | Usually not contagious |
| Main Cause | Poor water quality or gill irritation |
What You May See
| Behavior | Body Signs |
|---|---|
| Rapid breathing | Red swollen gills |
| Surface gasping | Gill cover opening wider |
| Weak swimming | Pale stressed body coloration |
| Reduced appetite | Heavy gill movement |
What To Check First
| Tank | Water | Recent Changes |
|---|---|---|
| Weak aeration | Ammonia spike | Large feeding spike |
| Dirty filter media | Nitrite poisoning | New fish added |
| Overcrowding | Low oxygen levels | Filter washed too aggressively |
Action Plan
What To Do Now
| Time | Action |
|---|---|
| Immediately | Increase aeration and surface movement |
| Immediately | Perform partial water change |
| Immediately | Test ammonia and nitrite |
| Next 24 Hours | Monitor breathing and swimming recovery |
Important Warnings
- Gill damage can worsen very quickly in low oxygen water.
- Do not overdose medication without confirming infection.
- Ammonia and nitrite poisoning commonly damage gills.
- High temperatures worsen oxygen stress.
- Severe gill damage may become irreversible.
Recommended Product Direction
Irritation Risk
Parasite Related
Flukes / Slime Coat
Heavy mucus, flashing, clamped fins, or irritated gills.
Irritation Risk
Parasite Related
Flukes / Slime Coat
Heavy mucus, flashing, clamped fins, or irritated gills.
Identification
What It Is
| Common Names | Gill Flukes, Skin Flukes, Slime Coat Irritation |
| Spread Risk | Medium to High |
| Main Cause | External parasites or heavy skin and gill irritation |
What You May See
| Behavior | Body Signs |
|---|---|
| Flashing or scratching | Thick cloudy slime coat |
| Rapid breathing | Red or irritated gills |
| Clamped fins | Cloudy patches on skin |
| Surface gasping | Excess mucus around gills |
What To Check First
| Tank | Water | Recent Changes |
|---|---|---|
| New fish introduced | Ammonia or nitrite present | No quarantine used |
| Overcrowding | Poor oxygen exchange | Added plants or livestock recently |
| Dirty substrate | Cloudy or unstable water | Recent transport stress |
Action Plan
What To Do Now
| Time | Action |
|---|---|
| Immediately | Increase aeration and surface movement |
| Immediately | Check ammonia, nitrite, and temperature |
| 24 Hours | Observe flashing, breathing, and slime coat |
| 2–7 Days | Use parasite treatment if flukes are strongly suspected |
Important Warnings
- Flukes can spread between fish.
- Gill flukes can cause serious breathing distress.
- Increase aeration during treatment.
- Remove activated carbon before medication.
- Do not confuse slime coat irritation with fungus.
Recommended Product Direction
Physical Damage
Injury Source
Mechanical Injury
Scrapes, torn fins, missing scales, red marks, body wounds, or injury after fighting, jumping, netting, sharp décor, or filter intake accidents.
Physical Damage
Injury Source
Mechanical Injury
Scrapes, torn fins, missing scales, red marks, body wounds, or injury after fighting, jumping, netting, sharp décor, or filter intake accidents.
Identification
How To Identify
- Clear scrape, torn fin, missing scale, damaged body area, or open wound.
- Usually affects one fish or one visible section of the body.
- Fish may hide, clamp fins, avoid food, or breathe faster after injury.
- Wound edges may turn red, white, fuzzy, or worsen if infection starts.
Most Likely Causes
- Fighting, chasing, bullying, or aggressive tankmates.
- Sharp rock, rough wood, unstable décor, or narrow gaps.
- Jumping injury, poor netting, transport damage, or handling stress.
- Filter intake damage or fish trapped behind equipment.
What To Check First
| Check | What To Look For | Action |
|---|---|---|
| Water Quality | Ammonia, nitrite, dirty water, high organic waste. | Test water. Keep ammonia/nitrite at 0 ppm. |
| Tankmates | Chasing, nipping, territorial fish, injured weaker fish. | Separate bully or injured fish if needed. |
| Hardscape | Sharp rock edges, rough wood, narrow gaps, unstable décor. | Remove, sand down, reposition, or block unsafe areas. |
| Wound Condition | Redness, swelling, white film, cotton growth, spreading damage. | Treat as secondary bacterial or fungal infection if worsening. |
Action Plan
Immediate Action
- Move injured fish to quarantine if weak, bullied, bleeding, or worsening.
- Remove sharp décor, unsafe hardscape, or aggressive tankmates.
- Improve water quality with a controlled water change.
- Increase aeration and keep the tank stable.
- Check the wound daily for redness, fungus, swelling, or spreading damage.
Treatment Direction
- Minor clean wounds often recover with stable water and low stress.
- Use antibacterial support if the wound turns red, swollen, ulcerated, or spreads.
- Use antifungal support if cotton-like growth appears on the wound.
- Avoid repeated netting, chasing, or unnecessary handling.
- Do not return fish until bullying or the injury source is fixed.
Product Direction
High Spread Risk
Common
White Spot (Ich)
Salt-like white spots appearing across the body and fins.
High Spread Risk
Common
White Spot (Ich)
Salt-like white spots appearing across the body and fins.
Identification
What It Is
| Common Names | Ich, White Spot Disease, External Parasite |
| Spread Risk | Very High |
| Quarantine | Strongly Recommended |
What You May See
| Behavior | Body Signs |
|---|---|
| Scratching | Small white salt-like dots |
| Rapid breathing | Dots spreading across fins |
| Hiding | Clamped fins |
| Reduced appetite | Stress coloration |
What To Check First
| Tank | Water | Recent Changes |
|---|---|---|
| Overcrowding | Ammonia or nitrite spike | Added new fish |
| Weak aeration | Temperature swings | No quarantine used |
| Stress from aggression | Dirty substrate | Recent transport stress |
Action Plan
What To Do Now
| Time | Action |
|---|---|
| Immediately | Increase aeration and perform partial water change |
| Immediately | Remove activated carbon before medication |
| 24 Hours | Monitor spread and breathing condition |
| 2–7 Days | Continue treatment according to medication instructions |
Important Warnings
- Remove carbon before treatment.
- Increase aeration during medication.
- Medication may affect shrimp and sensitive species.
- Do not overdose medication.
- White spots may continue appearing during early treatment.
Recommended Product Direction
External Parasite
Fast Spread
Velvet Disease
Fine gold, yellow, rust, or dusty coating on the body or fins. Fish may scratch, clamp fins, gasp, hide, or decline quickly.
External Parasite
Fast Spread
Velvet Disease
Fine gold, yellow, rust, or dusty coating on the body or fins. Fish may scratch, clamp fins, gasp, hide, or decline quickly.
Identification
How To Identify
- Fine gold, yellow, brown, or rust-like dust on body or fins.
- Usually easier to see under angled light or flashlight.
- Fish may rub against objects, clamp fins, hide, or breathe fast.
- Can spread quickly and affect multiple fish in the tank.
Most Likely Causes
- New fish introduced without quarantine.
- Parasite outbreak triggered by stress or unstable water.
- Low immunity after transport, temperature swing, or poor conditions.
- Cross-contamination from plants, water, nets, or shared tools.
What To Check First
| Check | What To Look For | Action |
|---|---|---|
| Lighting Angle | Gold dust, rusty shimmer, yellow powder, fine coating. | Use flashlight from the side or above. |
| Breathing | Fast gill movement, surface gasping, fish staying near flow. | Increase aeration immediately. |
| Spread | Multiple fish scratching, clamping, hiding, or losing appetite. | Treat the affected tank, not only one fish. |
| Water Quality | Ammonia, nitrite, dirty water, unstable temperature. | Test water and correct unsafe readings before treatment. |
Action Plan
Immediate Action
- Increase aeration before medication.
- Dim or switch off aquarium lights during treatment.
- Remove activated carbon or chemical media before dosing medication.
- Treat the whole affected tank if multiple fish show symptoms.
- Follow the full medication course. Do not stop early.
Treatment Direction
- Use velvet / external parasite medication suitable for aquarium fish.
- Copper-based treatment may be effective but must be used carefully.
- Do not use copper in tanks with shrimp, snails, or sensitive invertebrates.
- Move invertebrates out only if the treatment plan allows safe separation.
- After treatment, perform water change and restore chemical media if needed.
Product Direction
Bacterial Infection
Water Quality
Fin Rot
Frayed, torn, melting, cloudy, red, black, or receding fin edges. Often linked to poor water, stress, bullying, injury, or weakened fish.
Bacterial Infection
Water Quality
Fin Rot
Frayed, torn, melting, cloudy, red, black, or receding fin edges. Often linked to poor water, stress, bullying, injury, or weakened fish.
Identification
How To Identify
- Fin edges look ragged, uneven, white, red, black, or cloudy.
- Fins may shorten over time instead of healing.
- Fish may clamp fins, hide, breathe faster, or lose appetite.
- Severe cases may reach the fin base and become body infection.
Most Likely Causes
- Poor water quality, dirty substrate, or high organic waste.
- Fin nipping, fighting, rough handling, or mechanical injury.
- Stress from overcrowding, unstable temperature, or weak filtration.
- Untreated minor wounds turning into bacterial infection.
What To Check First
| Check | What To Look For | Action |
|---|---|---|
| Water Quality | Ammonia, nitrite, dirty water, high nitrate, waste buildup. | Test water. Keep ammonia/nitrite at 0 ppm. |
| Fin Edges | White rim, red streaks, blackened tips, melting or receding fins. | Track daily. Treat if damage spreads. |
| Tankmates | Nipping, chasing, bullying, territorial attacks. | Separate bully or injured fish. |
| Injury Source | Sharp décor, rough hardscape, filter intake, handling damage. | Remove or adjust the cause before treatment. |
Action Plan
Immediate Action
- Improve water quality with a controlled water change.
- Remove waste, uneaten food, and trapped debris.
- Separate fish if bullying, fin nipping, or repeated damage is seen.
- Increase aeration during recovery.
- Monitor whether fin loss stops or continues spreading.
Treatment Direction
- Minor fin damage may recover with clean, stable water.
- Use antibacterial treatment if fins keep receding, redden, or look infected.
- Move weak fish to quarantine if it cannot compete or is being attacked.
- Do not combine multiple medications unless product directions allow it.
- Continue observation until new clear fin growth appears.
Product Direction
Fungal Growth
Secondary Infection
Fungal Infection
White, grey, or cotton-like growth on wounds, fins, mouth, eggs, or damaged skin. Often follows injury, stress, poor water, or untreated infection.
Fungal Growth
Secondary Infection
Fungal Infection
White, grey, or cotton-like growth on wounds, fins, mouth, eggs, or damaged skin. Often follows injury, stress, poor water, or untreated infection.
Identification
How To Identify
- Cotton-like white, grey, or fluffy growth on body, fins, mouth, or wound area.
- Usually attached to damaged skin, injury site, dead tissue, or eggs.
- Fish may clamp fins, hide, breathe faster, or stop eating.
- Can spread if water is dirty or the wound remains untreated.
Most Likely Causes
- Mechanical injury, fin rot, mouth damage, or open wound.
- Poor water quality, high organic waste, or dirty substrate.
- Dead eggs, dead fish, uneaten food, or decaying material left in tank.
- Weak immunity after stress, transport, bullying, or unstable conditions.
What To Check First
| Check | What To Look For | Action |
|---|---|---|
| Growth Texture | Cotton, fluff, white-grey hair, fuzzy patch. | Treat as fungal if clearly cotton-like. |
| Original Injury | Scrape, torn fin, wound, mouth damage, ulcer, fin rot. | Treat the wound source, not only the fungus. |
| Water Cleanliness | Waste buildup, dead eggs, uneaten food, dirty substrate. | Remove decay and improve water quality. |
| Spread Speed | Patch enlarging, fish weakening, redness under fungus. | Quarantine and medicate promptly. |
Action Plan
Immediate Action
- Remove dead fish, dead eggs, uneaten food, and decaying waste.
- Move affected fish to quarantine if weak, bullied, or badly infected.
- Improve water quality with a controlled water change.
- Increase aeration during treatment.
- Check for injury, fin rot, mouth rot, or bacterial infection under the fungus.
Treatment Direction
- Use antifungal treatment for cotton-like external growth.
- Use antibacterial support if redness, swelling, ulcers, or fin rot are present.
- Do not scrape fungus off the fish manually.
- Do not stop treatment once the fungus shrinks; complete the product course.
- Keep water clean after treatment to prevent return.
Product Direction
Severe Internal Condition
Poor Prognosis
Dropsy
Swollen belly or body with raised pinecone scales. Often linked to internal bacterial infection, organ failure, severe stress, or poor water conditions.
Severe Internal Condition
Poor Prognosis
Dropsy
Swollen belly or body with raised pinecone scales. Often linked to internal bacterial infection, organ failure, severe stress, or poor water conditions.
Identification
How To Identify
- Body looks swollen, bloated, or rounded from the side and top.
- Scales stick outward like a pinecone, especially when viewed from above.
- Fish may stop eating, hide, clamp fins, breathe fast, or sit at the bottom.
- Severe cases may show pop-eye, red patches, ulcers, or stringy waste.
Most Likely Causes
- Internal bacterial infection or organ failure.
- Long-term poor water quality or unstable tank conditions.
- Stress from overcrowding, bullying, temperature swings, or weak filtration.
- Secondary condition after untreated infection, injury, or parasite stress.
What To Check First
| Check | What To Look For | Action |
|---|---|---|
| Pinecone Scales | Raised scales sticking outward when viewed from above. | Quarantine immediately. Treat as severe. |
| Swelling Pattern | Whole body swelling, not just normal egg-carrying or feeding belly. | Compare from top and side view. |
| Water Quality | Ammonia, nitrite, high nitrate, dirty substrate, waste buildup. | Test water and correct unsafe readings. |
| Other Symptoms | Pop-eye, ulcers, red patches, clamped fins, appetite loss. | Use internal antibacterial treatment direction. |
Action Plan
Immediate Action
- Move affected fish to a clean quarantine tank immediately.
- Increase aeration and keep water stable.
- Test ammonia, nitrite, nitrate, and temperature.
- Perform a controlled water change if water quality is unsafe.
- Do not return fish to the main tank while swelling or pinecone scales remain.
Treatment Direction
- Use internal antibacterial treatment as early as possible.
- Use aquarium salt or Epsom salt only if suitable for the fish species and product plan.
- Do not overfeed. Remove uneaten food quickly.
- Keep treatment simple. Do not mix multiple medicines unless directions allow it.
- Prognosis is poor once pinecone scales are clearly visible.
Product Direction
Eye Swelling
Injury / Infection
Pop-eye
One or both eyes look swollen, cloudy, bulging, or protruding. Often linked to injury, poor water, bacterial infection, or internal illness.
Eye Swelling
Injury / Infection
Pop-eye
One or both eyes look swollen, cloudy, bulging, or protruding. Often linked to injury, poor water, bacterial infection, or internal illness.
Identification
How To Identify
- Eye sticks out more than normal or looks swollen.
- Eye may look cloudy, white, red, scratched, or enlarged.
- One-eye cases often point to injury or local infection.
- Both-eye cases often point to water quality or internal infection.
Most Likely Causes
- Physical injury from fighting, netting, jumping, or hardscape impact.
- Poor water quality, high waste, ammonia, nitrite, or unstable conditions.
- Bacterial infection affecting eye tissue or internal organs.
- Advanced illness linked with dropsy, ulcers, or systemic infection.
What To Check First
| Check | What To Look For | Action |
|---|---|---|
| One Eye Or Both | One swollen eye versus both eyes swollen. | One eye: check injury. Both eyes: check water/internal infection. |
| Eye Surface | Cloudy eye, red eye, scratch, white film, bleeding, damage. | Treat as injury or bacterial infection if worsening. |
| Water Quality | Ammonia, nitrite, high nitrate, dirty water, waste buildup. | Test water. Keep ammonia/nitrite at 0 ppm. |
| Other Symptoms | Swollen body, pinecone scales, ulcers, appetite loss, clamped fins. | Quarantine and treat as severe internal infection. |
Action Plan
Immediate Action
- Move affected fish to quarantine if eye swelling is severe or worsening.
- Test ammonia, nitrite, nitrate, and temperature immediately.
- Improve water quality with a controlled water change if readings are unsafe.
- Remove sharp décor, bullying fish, or injury source if one-eye damage is likely.
- Increase aeration during recovery or medication.
Treatment Direction
- Minor injury-based pop-eye may improve with clean, stable water.
- Use antibacterial treatment if swelling, cloudiness, redness, or infection worsens.
- Treat both-eye pop-eye as higher risk, especially with appetite loss or body swelling.
- Check for dropsy if pop-eye appears with swollen body or raised scales.
- Do not handle or press the eye area.
Product Direction
Head Erosion
Internal Parasite Link
Hole-in-the-Head
Small pits, holes, wounds, or erosion around the head, face, and lateral line. Common in cichlids, discus, oscars, and large freshwater fish.
Head Erosion
Internal Parasite Link
Hole-in-the-Head
Small pits, holes, wounds, or erosion around the head, face, and lateral line. Common in cichlids, discus, oscars, and large freshwater fish.
Identification
How To Identify
- Small holes, pits, or crater-like marks on the head or face.
- Marks may spread along the lateral line.
- Fish may lose appetite, darken, hide, or produce stringy waste.
- Advanced cases show open wounds, white edges, or secondary infection.
Most Likely Causes
- Poor water quality, dirty filter, high organic waste, or long-term stress.
- Internal parasites or gut irritation, especially with stringy white waste.
- Low-quality diet, weak nutrition, or long-term vitamin deficiency.
- Overcrowding, unstable tank conditions, or poor maintenance routine.
What To Check First
| Check | What To Look For | Action |
|---|---|---|
| Head Marks | Pits, holes, face erosion, open wounds, white-edged lesions. | Track size and spread daily. |
| Waste | White, clear, stringy, or unusual faeces. | Consider internal parasite treatment direction. |
| Water Quality | Ammonia, nitrite, high nitrate, dirty filter, waste buildup. | Test water and improve maintenance immediately. |
| Diet | Poor appetite, single-food diet, low nutrition, old food. | Improve food quality and variety. |
Action Plan
Immediate Action
- Test ammonia, nitrite, nitrate, and temperature.
- Perform controlled water changes to reduce waste load.
- Clean filter media gently using old tank water.
- Remove trapped waste from substrate and feeding areas.
- Move fish to quarantine if wounds are open, infected, or worsening fast.
Treatment Direction
- Use internal parasite treatment if stringy white waste or appetite loss is present.
- Use antibacterial support if pits become red, swollen, ulcerated, or infected.
- Improve diet with higher-quality food and vitamin support.
- Reduce stress from bullying, overcrowding, or unstable water.
- Recovery is slow. Holes may take time to close after the cause is fixed.
Product Direction
Fast Bacterial Infection
Urgent Action
Columnaris
White mouth, pale saddle patch, body lesions, frayed fins, or fast skin damage. Often worsens quickly in stressed fish.
Fast Bacterial Infection
Urgent Action
Columnaris
White mouth, pale saddle patch, body lesions, frayed fins, or fast skin damage. Often worsens quickly in stressed fish.
Identification
How To Identify
- White, grey, or pale patch on mouth, head, back, body, or fins.
- May look flatter, slimy, or patchy instead of fluffy.
- Common signs: cotton mouth, saddleback patch, fin erosion, ulcers.
- Fish may clamp fins, breathe fast, hide, stop eating, or die suddenly.
Most Likely Causes
- Poor water, transport stress, overcrowding, bullying, or temperature swing.
- High organic waste, dirty filter, weak oxygen, or unstable tank conditions.
- Injury, fin damage, slime coat damage, or untreated external infection.
- Spread from infected fish, shared nets, tools, or quarantine failure.
What To Check First
| Check | What To Look For | Action |
|---|---|---|
| Patch Type | White mouth, pale saddle patch, flat grey film, body lesion. | Treat fast. Do not wait for it to spread. |
| Breathing | Fast gill movement, surface gasping, weak swimming. | Increase aeration immediately. |
| Spread Speed | Patch enlarges within hours or affects multiple fish. | Quarantine affected fish and treat urgently. |
| Water Quality | Ammonia, nitrite, high nitrate, dirty water, warm stagnant tank. | Test water and correct unsafe readings. |
Action Plan
Immediate Action
- Move affected fish to quarantine if possible.
- Increase aeration before medication.
- Remove activated carbon or chemical media before dosing.
- Test ammonia, nitrite, nitrate, and temperature.
- Avoid chasing, handling, overcrowding, or sudden temperature changes.
Treatment Direction
- Use antibacterial medication suitable for Columnaris / external bacterial infection.
- Treat early. Advanced cases can decline very quickly.
- Keep water clean and oxygen high during treatment.
- Do not raise temperature unless the medication specifically requires it.
- Complete the full course even if patches reduce.
Product Direction
Medication Safety
Medication & Treatment Notes
Check these points before dosing. Treat in quarantine when possible.
Before Medication
- Remove activated carbon / Purigen
- Increase aeration
- Confirm ammonia and nitrite first
- Do not mix medications blindly
During Treatment
- Follow label dosage
- Re-dose only after water change if required
- Watch breathing closely
- Keep lights low for sensitive meds
Sensitive Livestock
- Shrimp
- Snails
- Scaleless fish
- Some plants may be affected
- Use quarantine when possible
When Medication Fails
- Wrong diagnosis
- Poor oxygen
- Biofilter crash
- Fish already too weak
- Secondary infection
When Isolation Becomes Necessary
Some situations are safer to handle outside the main aquarium — especially contagious symptoms, breathing stress, severe injuries, repeated bullying, or medications that may affect shrimp, plants, or sensitive livestock.
Basic Setup
- Bare tank or clean tub
- No substrate
- PVC pipe / simple hide
- Heater if needed
Water Routine
- Test ammonia daily
- Test nitrite daily
- Remove waste daily
- Small water changes as needed
Air & Filter
- Sponge filter preferred
- Extra air stone
- No carbon during medication
- Add bacteria support if new
Use When
- Breathing stress
- Contagious symptoms
- Severe fin or body damage
- Medication unsafe for display tank
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