One day your fish look perfectly healthy—then suddenly, they’re flashing, hiding, or worse. Sound familiar? Aquarium diseases can strike fast. From mysterious spots to sudden behavior changes, if you don’t know what to look for, things can spiral quickly. But don’t panic—many of the most common fish illnesses are treatable once you know the signs. Let’s break down the usual troublemakers in your tank, what to watch for, and how to fight back before they take over.
1. Ich (White Spot Disease)
• Cause: Protozoan parasite (Ichthyophthirius multifiliis)
• Symptoms: White spots, flashing (rubbing against objects), lethargy
• Treatment:
• Raise temperature (if safe for species)
• Use meds like Ich-X, ParaGuard, Super Ick Cure
• Add aquarium salt (if fish tolerate it)
• Daily gravel vacs and water changes
2. Fin Rot
• Cause: Bacterial infection, often stress-related or from poor water
• Symptoms: Torn, ragged, or black-edged fins
• Treatment:
• Improve water quality immediately
• Use antibacterial meds like API Melafix or Kanaplex
• Add aquarium salt
• Remove aggressive tankmates if applicable
3. Velvet (Oodinium)
• Cause: Dinoflagellate parasite
• Symptoms: Gold or rust-colored dust on skin, clamped fins, rapid breathing
• Treatment:
• Dim the lights (parasite is photosynthetic)
• Use copper-based meds or API General Cure
• Raise temperature gradually
• Quarantine infected fish
4. Columnaris
• Cause: Bacteria (Flavobacterium columnare)
• Symptoms: Cottony patches, ulcers, gill damage, white lines on body
• Treatment:
• Kanaplex or Furan-2 in quarantine
• Lower water temp slightly (to slow spread)
• Improve oxygenation
5. Dropsy
• Cause: Internal infection, often kidney failure from bacteria
• Symptoms: Swollen body, pinecone-like scales, lethargy
• Treatment:
• Quarantine immediately
• Use Kanaplex or Epsom salt baths to draw out fluid
• Rarely curable in late stages
6. Swim Bladder Disease
• Cause: Overfeeding, constipation, infection
• Symptoms: Fish floats upside down or sinks, has trouble swimming
• Treatment:
• Fast for 2–3 days
• Feed shelled peas or high-fiber food
• Reduce water flow
7. Fungal Infections
• Cause: Secondary infection from wounds or stress
• Symptoms: White cottony growths
• Treatment:
• API Fungus Cure, Melafix, or Salt baths
• Address the underlying cause (injury, poor water)
8. Gill Flukes / Skin Flukes
• Cause: Microscopic parasitic worms
• Symptoms: Gasping at surface, rubbing, clamped fins, Layer of mucus covering gills or body, Chewed on or eaten-away gills or fins.
• Treatment:
• PraziPro or API General Cure
• Quarantine and increase aeration
Keeping fish healthy isn’t just about water changes and feeding routines—it’s also about knowing the early warning signs when something goes wrong. The more familiar you are with common aquarium diseases, the faster you can act—and the better your chances of saving your fish. With a sharp eye, a little preparation, and the right treatments on hand, you’ll be ready to handle whatever comes swimming your way.