Ich (Ichthyophthirius) presents as distinct, salt-grain-sized white spots scattered across the body and fins — like sprinkled salt. Velvet (Oodinium) appears as a fine golden, rust-colored, or grey dust-like coating, often visible only under angled light. Velvet typically causes more severe rubbing (flashing) and rapid breathing. A simple test: shine a flashlight at an angle — velvet gives a metallic sheen.

Flashing (scratching against rocks, substrate, or decorations) is a key sign of external parasites like Ich, Velvet, Anchor Worms, or Gill Flukes. It can also indicate poor water quality (high ammonia/nitrite) causing skin irritation. Always test your water parameters first, then inspect for visible parasites. If multiple fish are flashing, parasitic infection is the most likely culprit.

Dropsy (fluid retention causing pinecone-like raised scales) is a symptom of organ failure, often from bacterial infection. Early detection is critical. If caught before scales fully protrude, treatment with broad-spectrum antibiotics (like Kanamycin) combined with Epsom salt baths (1 tsp per gallon) can sometimes reverse it. Advanced cases with severe pineconing have a very low survival rate. Always isolate affected fish immediately.

Swim bladder issues can stem from: constipation (most common in goldfish), bacterial infection, physical injury, or genetic defects (especially in fancy goldfish and bettas). Start by fasting the fish for 2-3 days, then feed a blanched pea (skin removed). If this doesn't help, consider antibiotic treatment. For chronic cases, lowering water depth and providing resting spots near the surface can improve quality of life.

Set up a separate quarantine/hospital tank (10-20 gallons) with: a heater, gentle sponge filter (no carbon if medicating), hiding spots (PVC pipe or clay pot), and subdued lighting. Match the water parameters to the main tank initially. Observe for 2-4 weeks. Never use carbon filtration during medication — it removes most treatments. Perform daily small water changes (10-20%) to maintain pristine conditions.

Fin rot itself is typically a secondary bacterial infection triggered by stress or poor water quality. The bacteria (often Aeromonas or Pseudomonas) can spread to other fish, especially those with compromised immune systems or damaged fins. However, fin rot is rarely the primary contagion — it usually signals an underlying water quality issue. Fix the water first, then treat with antibacterial medication. Salt baths can help mild cases.

This is a common misdiagnosis. True fungus (Saprolegnia) appears as fluffy, cotton-like tufts, usually white or grey, often on injured areas. Columnaris (Flexibacter) is a bacterial infection that mimics fungus — it creates flat, dull white/grey patches, often around the mouth ("cotton mouth") or as a "saddleback" lesion across the back. Columnaris spreads rapidly and requires antibiotic treatment, not antifungal medication. Look closely: fungus is 3D and fluffy; Columnaris is flat and patchy.