Red Sore Disease Aquarium Treatment: Aeromonas Recognition

Red sore disease is one of those problems that creeps in quietly, then announces itself with raw, ulcerating patches on a previously healthy fish overnight. Effective red sore disease aquarium treatment hinges on recognising Aeromonas hydrophila early, because by the time the haemorrhagic lesion is fully open the secondary fungal load is often what kills the fish. This guide from Gensou Aquascaping at 5 Everton Park draws on a decade of treating outbreaks in HDB community tanks fed by warm, soft PUB water, the exact conditions in which opportunistic Aeromonas species thrive.

What Aeromonas Actually Is

Aeromonas is a Gram-negative motile rod that lives in essentially every freshwater system on the planet, including yours. It is opportunistic rather than introduced, which means infections almost always trace back to a stressor that compromised the fish first. Chronic ammonia exposure, low oxygen, rough handling and chilling all suppress the mucous immune barrier and let resident bacteria penetrate.

Recognising the Lesion Early

The classic red sore starts as a small, slightly raised pink patch under a single scale, often near the lateral line or at the base of a fin. Within 24 to 48 hours the scale lifts, the underlying tissue ulcerates, and a pale ring of dying epidermis surrounds a red, weeping centre. Goldfish, koi and large cichlids are most often affected in our climate. If you see two or more fish with similar marks in the same tank, treat it as a system-level water quality failure rather than a one-off injury.

Differential Diagnosis Matters

Not every red mark is Aeromonas. Columnaris produces white-grey saddle lesions that lack the haemorrhagic centre, and trauma from a heater burn or net injury looks similar but does not spread. Our columnaris fish treatment guide and the common fish diseases reference will help you separate them. Misidentifying columnaris as red sore wastes the critical first 48 hours on the wrong drug.

First Response in the Display Tank

Before any medication, address water quality. Test ammonia, nitrite and nitrate, and run a 30 to 40 percent water change with temperature-matched, dechlorinated PUB water. Singapore tap arrives chloramine-treated, so use Seachem Prime or an equivalent that binds both chlorine and ammonia. Drop the temperature by one or two degrees if your ambient allows; Aeromonas replicates faster at 30 to 32 degrees Celsius than at 26 to 27.

Moving the Fish to a Hospital Tank

Antibiotic therapy works far better in a dedicated hospital tank than in the display. A bare 40 to 60 litre tub with a sponge filter cycled from the main system, a heater set to 26 degrees, and gentle aeration is enough. Our hospital tank setup guide walks through the basics. Treating in the display kills your nitrifying bacteria, contaminates substrate with antibiotic residues, and exposes shrimp and snails unnecessarily.

Antibiotic Choices Available in Singapore

For confirmed Aeromonas, the gold standard is a combination of kanamycin and nitrofurazone, sold here as API Furan-2 paired with Seachem KanaPlex. Both are stocked at C328 Clementi, Y618 and several Thomson Road shops; expect to pay around $25 to $32 per bottle. Dose KanaPlex at one level scoop per 20 gallons every 48 hours for three doses, with a 25 percent water change between doses. Add Furan-2 simultaneously per the box dosing. Erythromycin alone is largely ineffective against Gram-negative rods and should not be the first choice.

Salt as a Supportive Therapy

Aquarium salt at 1 to 3 grams per litre supports osmoregulation, eases the metabolic burden on damaged tissue, and discourages secondary fungal colonisation. Use plain non-iodised salt only; the aquarium salt guide covers the correct ramping schedule. Avoid salt in tanks containing scaleless fish or sensitive plants beyond very low doses, and never add it to a hospital tank already running methylene blue baths.

Methylene Blue Dips for Open Wounds

For deep ulcers, a daily five-minute methylene blue dip at 50 mg per litre in a separate container accelerates healing and reduces fungal opportunists. The methylene blue treatment guide details the dip protocol. Net the fish gently, support the body in cupped hands rather than scooping, and watch for stress signs; if the gills clamp or the fish rolls, end the dip immediately.

Feeding Through the Treatment

A sick fish that stops eating loses condition rapidly in a tropical tank because metabolism remains high. Offer small amounts of medicated food soaked in garlic juice or a vitamin supplement; many Singapore reefers and freshwater keepers use the same Seachem Focus binder approach for both systems. If the fish refuses, do not panic on day one or two, but if refusal extends beyond 96 hours your prognosis worsens markedly.

Preventing the Next Outbreak

Once the fish recovers, the real work begins. Outbreaks rarely happen in tanks with stable parameters, light stocking, weekly water changes and proper quarantine of new arrivals. Review your routine against our community tank disease prevention guide, and consider whether your bioload, filter capacity, or feeding regimen put your fish under chronic low-grade stress. Aeromonas is always present; healthy fish simply outcompete it.

When to Stop Treatment

Continue antibiotics for the full course even if the lesion appears to scab over by day four. Stopping early breeds resistant strains and almost guarantees a relapse within two weeks. Once the fish has finished medication, run carbon for 48 hours to strip residual drugs, do a 50 percent water change, and only then return the fish to a properly cycled, well-maintained display.

Related Reading

• Columnaris Fish Treatment
• Common Fish Diseases Treatments
• How to Set Up Hospital Tank Beginners
• Aquarium Salt Guide Freshwater
• Aquarium Methylene Blue Treatment Guide