How to Deal With Ammonia in a New Tank: Emergency Steps

You set up your new tank, added fish and now your test kit is showing ammonia. Fish are gasping, acting stressed or hiding at the bottom. This is new tank syndrome — the biological filter has not matured enough to process the ammonia your fish produce. This ammonia new tank emergency guide from Gensou Aquascaping at 5 Everton Park tells you exactly what to do right now.

Step 1: Immediate Water Change

Perform a 50 per cent water change immediately using dechlorinated tap water at the same temperature as your tank. This is the single most effective action — it instantly halves the ammonia concentration. If ammonia is above 2 ppm, do a 70 per cent water change. Use Seachem Prime as your dechlorinator — it also temporarily detoxifies ammonia for 24–48 hours. Do not worry about removing beneficial bacteria — they live on surfaces and filter media, not in the water column.

Step 2: Dose a Detoxifier

After the water change, dose Seachem Prime at two to five times the normal amount (up to 5 ml per 40 litres). Prime converts toxic free ammonia (NH₃) into less harmful ammonium (NH₄⁺), which is still available for bacteria to consume but far less toxic to fish. This buys you 24–48 hours of safety. Repeat the Prime dose every 24–48 hours until ammonia stays at zero without treatment.

Step 3: Stop Feeding

Stop feeding your fish for two to three days. Fish can safely go several days without food, and every bit of food they eat becomes more ammonia. When you resume feeding, offer only a tiny pinch once daily until the tank is fully cycled. Overfeeding in a new tank is one of the primary drivers of ammonia crises.

Step 4: Maximise Aeration

Ammonia is more toxic at higher temperatures and lower oxygen levels. Increase surface agitation by lowering the filter outflow to splash the surface, or add an air stone with an air pump. Good oxygenation helps fish cope with ammonia stress and supports the aerobic bacteria that process ammonia.

Step 5: Add Beneficial Bacteria

Dose a quality bacterial supplement daily — Seachem Stability, Dr Tim’s One and Only, or Fritz Zyme 7 are all effective options available in Singapore. These products introduce live nitrifying bacteria that accelerate the cycling process. If you know another hobbyist with a healthy, established tank, ask for a piece of used filter sponge — this is the single most effective way to seed your filter with mature bacteria.

Step 6: Monitor Daily

Test ammonia daily until it reads zero on two consecutive days without dosing Prime. Continue daily 25–30 per cent water changes whenever ammonia exceeds 0.5 ppm. Keep a log of your readings to track progress. You should see ammonia start dropping within one to two weeks as the bacterial colony grows. Once ammonia hits zero, start monitoring nitrite — the next stage of the cycle.

What NOT to Do

Do not add more fish — the tank cannot handle its current bioload yet. Do not replace filter media — you need every bit of bacteria that is developing. Do not add ammonia-removing chemicals like zeolite permanently — they provide a temporary fix but prevent the natural bacterial colony from establishing. Do not shut off the filter, even at night — the bacteria need constant water flow and oxygen. Do not panic and do a 100 per cent water change — this is unnecessarily stressful for fish and not needed if you follow the steps above.

Preventing Future Ammonia Crises

Cycle the tank fully before adding fish — fishless cycling with pure ammonia takes three to six weeks but spares fish from any suffering. When adding fish to a cycled tank, add only three to five small fish per week to allow the bacterial colony to scale up gradually. Never clean more than one-third of your filter media at a time, and always rinse in old tank water, never tap water. Test weekly as a habit — catching a small rise at 0.25 ppm is much easier to handle than discovering a full crisis at 2 ppm.

Related Reading

• Your First 30 Days With a New Aquarium: Week-by-Week Guide
• Fishless Cycling With Pure Ammonia: Step-by-Step Guide
• How to Do a Fishless Cycle With Pure Ammonia: Step by Step
• 15 Mistakes New Aquarium Hobbyists Make and How to Avoid Them
• How to Build Confidence as a New Fishkeeper: First Year Milestones