Reput Sirip (Fin Rot Betta): Causes & Treatment for Bettas, Guppies & Goldfish

Fin rot betta keepers see it as ragged, shrinking fins with dark, white or red edges. In Malay it's called reput sirip or busuk sirip ikan. It is almost always a bacterial infection that takes hold when water quality drops or the fish is stressed. The fix has two parts: clean up the water first (test ammonia and nitrite, change water with anti klorin, keep the tank stable) and then, if the rot is still spreading after a few days, use a fin rot medication. Caught early, most bettas, guppies and goldfish recover and regrow their fins over weeks to months.

Is It Really Fin Rot? Quick Check

Not every damaged fin is fin rot. Before you reach for ubat ikan, compare what you see:

What you see	Likely cause	What it means
Ragged edges, dark/black, white or red margins, fins getting shorter	Fin rot	Bacterial infection; treat water and fish
Clean, sudden bites or chunks missing, edges look normal	Fin biting / nipping	Betta tail-biting (stress, boredom) or tankmates nipping
Fins curling at the tips, no discolouration	Fin curl	Often genetics or long-term water quality; not infectious
Torn fins after netting or decorations	Injury	Heals on its own in clean water
Fluffy white cotton on fin edges	Fungus (kulat)	Often follows fin rot; see the fungus guide
Rot reaching the body, red sores	Severe fin rot	Urgent; treat immediately

Halfmoon and long-finned bettas are especially prone to tail-biting, which looks similar. Tail-biting usually happens overnight and leaves clean edges, while fin rot creeps slowly and the edges change colour.

What Causes Fin Rot?

Fin rot is caused by bacteria that are normally present in every aquarium. They only attack when the fish's defences are down. Common triggers in Malaysian homes:

• Poor water quality: ammonia and nitrite from overfeeding, overcrowding or skipped water changes
• Small, unfiltered containers: betta bowls and jars that foul quickly
• Untreated tap water: chlorine damages fins and gills. The Ministry of Health standard allows free residual chlorine up to 5 mg/L in tap water, so always use anti klorin
• Temperature swings: tanks near windows or aircond vents
• Stress: bullying, fin-nipping tankmates, shipping
• Injuries from sharp plastic plants or rough decorations

Step-by-Step Fin Rot Treatment

Stage 1: Fix the water (days 1–3)

1. Test ammonia, nitrite and nitrate. A water test kit is essential here.
2. Do a 30–50% water change with temperature-matched, dechlorinated water.
3. For small betta tanks (under 1 kaki), change 30% daily or every other day until healed.
4. Remove sharp decorations and anything that tears fins.
5. Reduce feeding to small portions and remove leftovers.

Mild fin rot often stops spreading with clean water alone.

Stage 2: Mild supportive treatment (days 3–7)

If the edges are still discoloured but not advancing fast:

• Daun ketapang (catappa leaves): releases tannins and is a traditional betta remedy. It helps create soft, slightly acidic water that many bettas like. See the daun ketapang guide.
• Aquarium salt (garam ikan): for guppies, mollies and goldfish, a low dose can help. Use it carefully with bettas and don't use it in planted tanks or with scaleless fish. Our guide to garam ikan untuk apa gives safe doses.

Stage 3: Medication (if the rot keeps spreading)

If the rot reaches the body, spreads after 3–5 days of clean water, or the fish is lethargic, use a medication labelled for fin rot or bacterial infections. Options include products sold specifically as anti-fin-rot treatments and broad-spectrum antibacterial treatments. Find them under fish medication.

Rules for safe treatment:

• Treat in a separate hospital tank if possible, especially if you have shrimp, snails or plants
• Dose for the real water volume, not the nominal tank size
• Remove activated carbon from the filter during treatment
• Complete the full course on the label, even if the fish looks better
• Don't mix medications unless the label says it's safe

Methylene blue (ubat biru) is sometimes used for mild cases and fungus. See the ubat biru guide.

Stage 4: Recovery

Once rot stops, you'll see a clear or white band of new fin growing at the edge. That's healing, not fungus. Keep the water clean and avoid stress.

Fin Rot in Bettas, Guppies and Goldfish

Bettas (ikan laga)

Long fins and small containers make bettas the most common victims. Keep your betta in at least a filtered 1 kaki tank, with gentle flow so the fins aren't battered. Read the full betta care guide and the penyakit ikan laga guide.

Guppies (fin rot guppy)

Guppy tails are thin and showy. Fin rot in guppies often follows overcrowding and fin-nipping. Livebearers usually benefit from slightly harder water, and a low salt dose often helps. Separate males being chased constantly. See penyakit ikan guppy.

Goldfish (ikan emas)

Goldfish produce lots of waste, and fin rot often appears in crowded, under-filtered tanks, especially in Malaysian heat when bacteria multiply faster. Boost filtration, change water more often, and keep the tank cooler with a fan. See penyakit ikan emas.

How Long Do Fins Take to Regrow?

It depends on the fish and how much was lost:

• Mild damage: new growth visible in 1–2 weeks; fins look close to normal in about a month
• Moderate damage: 1–3 months
• Severe damage: regrowth can take several months, and fins may grow back slightly different in shape or colour

If rot reached the fin base, the fin may not fully regrow. In clean, warm Malaysian water (26–30°C), healing is usually faster than in cool water.

Prevention

• Weekly water changes with anti klorin, using water conditioners
• A filter appropriate for the tank size
• No overfeeding
• Silk or live plants instead of sharp plastic
• Avoid fin-nipping tankmates (tiger barbs and some tetras with bettas or guppies)
• Quarantine new fish

Frequently Asked Questions

Ubat apa untuk ikan laga reput sirip?

Mula-mula tukar air dan pastikan air bersih dengan anti klorin. Daun ketapang boleh membantu untuk kes ringan. Jika reput sirip terus merebak selepas beberapa hari, gunakan ubat ikan khas untuk fin rot atau jangkitan bakteria dan ikut dos pada label.

Sirip ikan laga boleh tumbuh balik ke?

Boleh, jika reput dihentikan awal. Sirip baru biasanya nampak lutsinar atau putih di hujung dalam masa 1–2 minggu. Kerosakan teruk boleh ambil masa beberapa bulan untuk pulih.

Kenapa sirip ikan guppy jadi koyak dan pendek?

Biasanya kerana air kotor, akuarium terlalu padat atau digigit ikan lain. Tukar air dengan kerap, kurangkan bilangan ikan dan asingkan ikan yang suka menggigit.

How do I tell fin rot from tail biting in bettas?

Fin rot spreads slowly with discoloured (dark, white or red) edges. Tail biting appears suddenly and leaves clean, sharp edges with no colour change.

Is fin rot contagious?

The bacteria are already in most tanks, so fin rot isn't "caught" like a virus. But the poor conditions that cause it affect every fish in the tank, so check all of them.