1
Water test
Check ammonia and nitrite first.
Burned gills and poisoning can look like disease. Positive ammonia or nitrite changes the plan immediately.
The Hidden ReefAquariums · Fish · Coral · Ponds
Sick fish guide
Parasites or Ich?
White spots, flashing, clamped fins, heavy breathing, and scratching can come from parasites, stress, or water quality. Check the basics first, then choose treatment based on symptoms and livestock safety.
- Salt-like spots Ich often looks like tiny white grains on fins or body.
- Flashing Scratching against decor can mean irritation, parasites, or poor water.
- Clamped fins A stress sign, not a diagnosis by itself.
- Heavy breathing Treat oxygen and water quality as urgent.
First response
Do this before medicating the tank.
The safest first move is to separate symptoms from water-quality emergencies.
2
Oxygen
Increase surface movement.
Add aeration or aim flow at the surface if fish are breathing hard, crowding filters, or hanging near the top.
3
Containment
Consider a hospital tank.
Medication is easier and safer in a bare treatment tank, especially with shrimp, snails, plants, coral, or live rock.
Visual clues
Separate ich from look-alikes.
The symptom pattern matters more than a single white mark.
Ich-like grains
Multiple tiny white spots that look like salt grains, especially with scratching, are a classic ich warning.
Fine dust or gold sheen
A powdery coating with rapid breathing can be more urgent than ordinary ich. Ask for help quickly.
Flashing and scratching
Scratching can come from parasites, chlorine exposure, ammonia, pH swings, or debris irritating the gills.
Clamped fins or hiding
These are warning signs, but they do not identify the disease. Combine them with tests and visible symptoms.
Cloudy eyes or ragged fins
Damage after parasites or poor water may need a different treatment path than ich alone.
Gasping or sudden losses
Treat this as urgent water quality, oxygen, temperature, toxin, or fast-moving parasite risk.
What to check next
Match symptoms before choosing treatment.
Use this before choosing medication or treating the whole tank.
Question
Likely direction
Next action
Are fish gasping or dying suddenly?
That is urgent, even if spots are present.
Increase aeration and test ammonia, nitrite, pH, and temperature first.
Are there many tiny salt-like spots?
Ich is possible when spots repeat across fins/body and fish scratch.
Move affected fish to treatment when possible and choose fish-safe medication.
Is it dust, slime, cotton, wounds, or fin damage?
Those can point away from basic ich.
Bring photos or video before mixing treatments.
Are invertebrates, plants, coral, or live rock present?
Many medications are unsafe for them.
Use a hospital tank or ask the store before dosing the display.
Common causes
What usually starts the outbreak?
Most sick-fish cases combine exposure, stress, and water conditions.
No quarantine period
New fish can bring parasites before symptoms are obvious. Quarantine catches problems before the display is exposed.
Weak immune response
Shipping, bullying, temperature swings, and poor acclimation can make fish more vulnerable to parasites.
Ammonia, nitrite, or pH trouble
Bad water can mimic disease and makes any real infection harder for fish to survive.
Unstable heat or chill
Temperature swings stress fish and can change how quickly parasite life cycles move.
Crowding and aggression
Fish that are chased, nipped, or overcrowded often show illness first because they cannot recover between stress events.
Wrong medication or mixed dosing
Guessing can delay the right fix and harm sensitive livestock. Identify the symptom pattern before dosing.
Helpful supplies
What you may need.
Start with diagnosis and safe treatment, not random medication stacking.
Ammonia, nitrite, pH, and temperature
These separate water emergencies from true disease and guide whether water changes come before medication.
Shop maintenanceHospital tank basics
A simple bare tank, heater, air-driven sponge filter, and cover make treatment cleaner and safer.
View aquariumsAir pumps and surface movement
Sick fish and medicated tanks often need extra oxygen support.
View filtrationIch and parasite treatments
Choose medication based on freshwater, saltwater, reef safety, and livestock sensitivity.
Shop maintenanceUV sterilizers
UV can help reduce free-floating organisms when sized correctly, but it does not replace treatment.
View UV clarifiersNets, containers, and specimen cups
Clear photos, short video, and careful isolation help the store identify the problem faster.
Shop maintenanceWhat to avoid
Do not mix multiple medications, dose reef displays blindly, or treat before checking ammonia and nitrite. Remove carbon only when the medication instructions call for it, and keep oxygen high during treatment.
Compare with the cloudy water guideOpen the quick-reference sick fish chart
