Air Akuarium Berbau: Why Your Fish Tank Smells & How to Fix It
A healthy aquarium should smell faintly earthy, like a garden after rain, or of almost nothing. If your air akuarium berbau (tank water smells) of rotten eggs, sewage, rotting fish or something sour, something in the tank is decaying faster than your filter can handle. The usual culprits are rotting food, a dead fish or snail, a dirty filter, or gas trapped in old gravel. Most smells clear within a day or two once you find and remove the source, do a water change and clean the filter properly.
Match the Smell to the Cause
| Smell | Likely cause | First action |
|---|---|---|
| Rotten eggs (sulfur) | Hydrogen sulfide from anaerobic pockets in deep sand or compacted gravel | Stir and siphon the substrate in sections |
| Rotting fish / meat | Dead fish, shrimp or snail; rotting frozen food | Search the tank; remove the body |
| Sewage / sour | Overfeeding, clogged filter, heavy waste | Water change, clean filter, feed less |
| Musty / mouldy | Rotting plants, wood or leaves | Remove dead leaves; check driftwood |
| Strong chemical | Medicine, fertiliser overdose, contamination | Water change; add carbon |
| Fishy, "pond-like" but mild | Normal in fish-heavy tanks | Keep up maintenance |
| Earthy | Healthy biological activity | Nothing |
Air Akuarium Berbau: Main Causes in Detail
Rotting food
In warm Malaysian water (27–31°C), uneaten food starts breaking down within hours. Frozen bloodworms and meaty foods smell worst. If you see food left on the bottom after a few minutes, you're feeding too much.
A dead fish, shrimp or snail
A small fish can disappear behind rocks, inside a cave or under the filter intake. Snails die quietly inside their shells and smell very strongly. Count your fish and lift decor. To test a snail, take it out and sniff it: a dead snail is unmistakable.
Dirty filter
Filter sponges trap waste. When they clog, water flow drops, oxygen in the filter falls and waste starts to rot inside. Rinse sponges in a bucket of old tank water, not tap water, which kills good bacteria. Replace worn media gradually. Find sponges and media in filter accessories.
Anaerobic gravel or sand
Deep, compacted sand or gravel with no oxygen can develop pockets where bacteria produce hydrogen sulfide, the rotten-egg gas. You may see black patches in the substrate or bubbles rising when you poke it. It's toxic to fish in quantity.
Fix: siphon and stir the substrate a section at a time over several water changes, not all at once. Keep sand layers fairly shallow, and add Malaysian trumpet snails if you like; they burrow and turn the sand.
Rotting plants, wood and leaves
Melting plants, too many daun ketapang leaves left to rot, or poorly prepared driftwood can sour the water. Remove dead leaves weekly. See our Malaysian driftwood guide for preparing wood.
Overstocking
Too many fish for the tank and filter means more waste than the system can process. Our tank size guide gives stocking examples.
Quick Fix: Step by Step
- Find and remove the source: dead animals, rotting food, dead plant matter.
- Do a 30–50% water change with water treated with anti klorin.
- Siphon the gravel in the dirtiest areas. Use a gravel vacuum from cleaning and maintenance.
- Rinse the filter sponge in old tank water.
- Add activated carbon to the filter. It absorbs odours and dissolved organics. Replace it every few weeks, since it stops working once full.
- Test ammonia and nitrite. A rotting body can cause a spike.
- Increase aeration while the water recovers.
- Feed lightly for a few days.
The smell should fade within a day. If it returns quickly, the source is still there.
Prevention
- Feed less: only what's eaten in a minute or two.
- Weekly water changes of 20–30%. See cara tukar air akuarium.
- Clean filter media regularly in tank water.
- Remove dead plant leaves and old ketapang leaves.
- Count your fish daily at feeding time.
- Don't overstock, and size the filter for the tank.
- Keep a lid to reduce smells spreading in small rooms and condos, and to stop fish jumping out and dying unnoticed behind the tank.
Does Aquarium Water Count as Najis?
Some Muslim readers ask whether aquarium water, which contains fish waste, is najis, especially when it splashes onto clothes or the floor. The Pejabat Mufti Wilayah Persekutuan addresses this in Al-Kafi #801. In summary, its stated view is that aquarium water that is less than two qullah and mixed with fish waste is treated as najis, so splashes should be cleaned until the smell, colour and texture are gone, while amounts too small to see with the naked eye are excused. Please read the full Al-Kafi #801 article on the Mufti WP website, and ask your state mufti office or a religious teacher for guidance on your own situation. This summary is not a ruling.
A practical tip: lay a towel under the bucket during water changes, and wipe splashes straight away.
FAQ
Kenapa air akuarium berbau busuk?
Biasanya sebab ada sisa makanan atau ikan dan siput mati yang reput, penapis yang kotor, atau gas yang terperangkap dalam pasir dan batu kerikil. Cari punca dan buang, tukar 30 hingga 50 peratus air dan cuci span penapis dengan air akuarium.
Bau telur busuk dalam akuarium, bahaya tak?
Ya, boleh bahaya. Bau telur busuk datang daripada gas hidrogen sulfida dalam pasir yang terlalu padat dan kurang oksigen. Gas ini beracun untuk ikan. Sedut dan gaul pasir sedikit demi sedikit setiap kali tukar air.
Why does my new tank smell?
New tanks can smell slightly while bacteria settle, and new driftwood or soil can add an earthy or woody smell. A strong, foul smell isn't normal. Test ammonia and nitrite.
Does activated carbon remove smell?
Yes, it absorbs many odours and dissolved organics, but it doesn't remove the cause. Use it after you've removed the source and done a water change, and replace it regularly.
Is it normal for a pond to smell?
A koi pond can smell slightly fishy or earthy. A sewage or rotten smell means too much waste, a dirty filter or poor circulation. Clean the filter, remove debris and do a partial water change.
Keep your tank fresh with cleaning and maintenance tools, filter media and water conditioners from Malaysian sellers on FishyHub.