Introduction
Keeping an aquarium is deeply rewarding—but it comes with the responsibility of maintaining a healthy environment for your fish. Even with regular care, disease outbreaks can still occur due to stress, poor water quality, or exposure to new pathogens. In this guide, our experts at Limited Edition Corals will help you identify common aquarium fish diseases, how to treat them effectively, and most importantly, how to prevent them.
Understanding Fish Health and Disease
The Importance of Observation
Fish can’t tell you when they’re sick, but they do show signs. Noticing symptoms early can prevent the disease from spreading and becoming fatal. Regular observation of behavior and appearance is your first defense.
Why Do Fish Get Sick?
Fish are vulnerable to a variety of stressors that weaken their immune system. The most common causes include:
Poor water quality: High ammonia or nitrite levels
Stress: Overcrowding, aggression, or sudden temperature changes
Lack of quarantine: New fish or plants carrying parasites
Symptoms to Watch For
Gasping at the surface or rapid gill movement
Unusual swimming behavior or loss of buoyancy
Frayed or deteriorating fins
White spots, bloating, or ulcers
Loss of appetite or hiding excessively
Common Aquarium Diseases and Their Treatments
Ich (White Spot Disease)
Symptoms: Tiny white spots, scratching on objects, clamped fins
Cause: Ichthyophthirius multifiliis (protozoan parasite)
Treatment:
Raise water temperature to 80–82°F
Use a commercial Ich treatment (formalin, malachite green)
Perform 25% water changes every other day
Fin Rot
Symptoms: Fin edges turn white or black, fins fray or disappear
Cause: Bacterial infection, often secondary to stress
Treatment:
Improve water quality
Use antibacterial medications like Maracyn
Remove aggressive tank mates
Velvet Disease
Symptoms: Gold or rust-colored dust on body, lethargy
Cause: Dinoflagellate parasite (Oodinium)
Treatment:
Dim tank lights (parasite needs light)
Use copper-based medications
Isolate infected fish
Dropsy
Symptoms: Swollen belly, scales sticking out like a pinecone
Cause: Internal bacterial infection or organ failure
Treatment:
Quarantine immediately
Administer broad-spectrum antibiotics
Improve water conditions
Swim Bladder Disease
Symptoms: Fish floating upside-down or sinking to the bottom
Cause: Constipation, infection, or injury
Treatment:
Fast the fish for 24–48 hours
Feed blanched peas to relieve constipation
Use antibiotics for infections
How to Set Up a Quarantine or Hospital Tank
Quarantine is one of the best ways to prevent introducing disease to your main display tank. It gives you time to observe new fish and treat minor infections without risk to other livestock.
Essentials for a Quarantine Tank
A 10–20 gallon bare-bottom tank
Sponge filter or gentle filtration
Heater and thermometer
Basic hiding decor
Test kits for ammonia, nitrites, and pH
Need help setting one up? Contact us for custom aquarium services tailored to your tank size and goals.
Best Treatment Practices
When and How to Medicate
Before adding any medication:
Remove activated carbon from your filter (it will absorb medications)
Dose exactly as per label instructions
Isolate infected fish if possible
Continue treatment even after symptoms fade
If you’re unsure, consult an expert. Our team at Limited Edition Corals is always happy to help.
Common Types of Treatments
Antibacterial: Maracyn, Kanaplex, Furan-2
Antiparasitic: CopperSafe, formalin, PraziPro
Natural options: Aquarium salt, Indian almond leaves, garlic extract
For fish keepers looking for in-depth treatment resources, we recommend these external sources:
Preventing Future Disease Outbreaks
Water Quality is Everything
Test water weekly for pH, ammonia, nitrites, and nitrates
Perform 20–30% water changes weekly
Avoid overfeeding and remove uneaten food
Use RO/DI water if needed, especially for marine tanks
Always Quarantine New Additions
Quarantine new fish for at least 2–4 weeks
Inspect and dip corals and plants to eliminate pests
Never share nets or equipment between tanks without cleaning
Balanced Nutrition and Tank Environment
Feed a variety of foods (flakes, frozen, live)
Reduce aggressive behavior with appropriate tank mates
Maintain stable temperature and lighting
Need expert help managing your system? We provide in-home aquarium maintenance throughout Arizona.
When to Ask for Professional Help
Some illnesses are persistent, and not all fishkeepers have time to manage advanced treatments. If you’re dealing with:
Recurrent infections
Mass fish loss
Difficult-to-identify symptoms
…then it’s time to call in the pros.
Our team at Limited Edition Corals can assist with aquarium health checks, water testing, and personalized disease treatment strategies. Contact us here.
Final Thoughts
Fish diseases can be challenging, but with the right tools and guidance, most cases are manageable. Prevention, early detection, and proper quarantine are your best defenses.
Need help selecting medications or setting up a hospital tank? Stop by Limited Edition Corals—Arizona’s top choice for saltwater aquarium care since 2007. Whether it’s equipment, advice, or a full-service setup, we’re here to help your aquatic ecosystem thrive.
👉 Visit us in Phoenix or explore our full list of aquarium services today.
Frequently Asked Questions (FAQs)
Should I remove sick fish from the main tank?
Yes, isolating a sick fish in a separate quarantine or hospital tank is strongly recommended. This helps prevent the spread of disease to healthy fish in your display aquarium. It also allows for targeted treatment, minimizing stress for the infected fish and avoiding unnecessary medication exposure for others. A simple 10-20 gallon setup with a heater, filter, and basic decor will work for most cases.
Can I treat the whole tank at once?
You can, but it’s generally not ideal. Treating the entire tank may harm beneficial bacteria that are essential for biological filtration, leading to water quality issues. Additionally, medicating healthy fish can cause stress and weaken their immune systems. Use whole-tank treatments only when the disease is widespread or if moving the fish isn’t possible.
How do I prevent Ich from coming back?
Ich is often introduced by new fish that weren’t properly quarantined. Prevent recurrence by quarantining all new fish for at least 2–4 weeks. Also, maintain consistent water temperature, avoid overcrowding, and perform regular water tests to ensure stable conditions. Clean any new decorations or plants before adding them to your tank.
Do I need special medications for saltwater fish?
Yes, saltwater fish often need copper-based or specialized marine-safe medications. Be cautious when treating tanks with corals or invertebrates, as they are sensitive to many common treatments. Always read labels carefully or consult an expert before using any product in a reef tank.
How can I tell if it’s a parasite or a bacterial infection?
Parasites typically cause symptoms like scratching, white spots, or erratic swimming. Bacterial infections usually result in open wounds, swelling, or fraying fins. When uncertain, take clear photos and seek help from professionals—like the experts at Limited Edition Corals.