How to Do a Fishless Cycle With Pure Ammonia: Step by Step
Setting up a new aquarium and adding fish the same day is one of the most reliable ways to lose them within a week. The nitrogen cycle — the biological process that converts toxic fish waste into relatively harmless nitrate — takes time to establish, and that process requires patience. The fishless cycle using ammonia is the most reliable and humane method for establishing this cycle before any fish enter the tank. This guide from Gensou Aquascaping at 5 Everton Park, Singapore walks you through every step, from sourcing the right ammonia to knowing when the cycle is genuinely complete.
Why the Nitrogen Cycle Matters
Fish excrete ammonia continuously through their gills and waste. In a new, uncycled tank, ammonia accumulates rapidly to toxic levels. The cycle works through two groups of beneficial bacteria: Nitrosomonas species convert ammonia to nitrite (also toxic), and Nitrospira species then convert nitrite to nitrate (much less toxic at low concentrations). Both bacterial colonies take time to grow to sufficient populations — typically three to six weeks from scratch. The fishless ammonia method feeds these bacteria before any fish are present, so your tank is ready for livestock from day one of stocking.
Sourcing the Right Ammonia
Not all ammonia products are suitable for aquarium cycling. You need pure ammonia solution — 10% ammonia in water, with no surfactants, no fragrances, and no colourants. In Singapore, Dr. Tims Ammonium Chloride is the most reliable dedicated aquarium product and is available from several specialist fish shops. Alternatively, some supermarket cleaning ammonia products work, but you must confirm they contain no additives: shake the bottle vigorously. If it foams or suds, do not use it — surfactants will harm beneficial bacteria and create persistent surface foam in your tank.
Setting Up Before You Dose
Fill your tank completely, dechlorinate the water with a quality conditioner (essential — chloramine in Singapore’s PUB tap water kills the beneficial bacteria you are trying to cultivate), and run your filter and heater for 24 hours before starting. Set the temperature to 28 to 30°C; warmer water accelerates bacterial growth and shortens the overall cycle time. You do not need substrate or plants to complete a fishless cycle, but if your final setup will include aquasoil, add it now — aquasoil leaches ammonia and nutrients initially, which factors into your dosing baseline.
Step-by-Step Dosing Protocol
Use a liquid test kit, not strips, for accuracy throughout this process. Begin by dosing ammonia to reach a concentration of 2 to 4 ppm. This is your target level to feed the bacteria. The exact volume of ammonia needed per litre varies by concentration of your ammonia solution — add a small amount, test, and adjust. For a 100-litre tank using 10% ammonia solution, roughly 0.5 to 1 ml typically brings ammonia to the 2 to 4 ppm range, but test rather than assume.
Test ammonia and nitrite daily. For the first week to ten days, expect ammonia to remain elevated with no nitrite detectable — the first bacterial colony is still establishing. When nitrite begins to rise, you know Nitrosomonas are active. Continue dosing ammonia every two to three days to keep it above 1 ppm. Eventually — often around week three to four — you will notice ammonia dropping faster and nitrite beginning to spike sharply, then start to fall as Nitrospira establish.
Reading the Progress Signs
The cycle is approaching completion when ammonia drops from 2 ppm to zero within 24 hours AND nitrite simultaneously drops to zero within the same period. At this stage, both bacterial colonies are large enough to process waste quickly. Test nitrate — it will have been accumulating throughout the cycle and may read 40 ppm or higher. Do a large water change (50%) to bring nitrate down below 20 ppm before stocking.
A common mistake is declaring the cycle complete when only ammonia drops to zero but nitrite remains elevated. This means only the first bacterial colony is fully established. Continue dosing and wait for both to hit zero simultaneously before adding fish.
Speeding Up the Cycle
Cycle time can be shortened significantly with bacterial supplements. Seachem Stability and Dr. Tim’s One and Only both contain live nitrifying bacteria cultures and can reduce cycle time to two to three weeks when used correctly. Adding a small amount of established filter media — sponge, ceramic rings, or even gravel — from a healthy, disease-free aquarium is the fastest method of all, sometimes cycling a new tank in as little as one week.
When You Can Add Fish
Once ammonia and nitrite both hit zero within 24 hours of a 2 ppm ammonia dose, and you have completed a partial water change to reduce nitrate, your tank is ready. Stock gradually — add no more than a quarter of your intended final stocking in the first week, then test daily for any ammonia or nitrite spike. The bacterial colony needs time to adjust to the bioload of living fish producing waste continuously rather than the periodic dosing of the cycling phase. Gensou Aquascaping offers water quality consultations for hobbyists setting up their first tanks in Singapore — get in touch if you need guidance through the process.
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