Fishless Cycling Step by Step: The Humane Way to Start

What Is Fishless Cycling and Why Does It Matter
What You Need Before You Start
Choosing Your Ammonia Source
Step-by-Step Fishless Cycling Process
Understanding the Nitrite Spike Phase
When Is the Cycle Complete
Speeding Up the Cycle
Common Mistakes to Avoid
Frequently Asked Questions

Setting up a new aquarium is exciting, but the single most important thing you can do before adding fish is to cycle the tank. Fishless cycling establishes the beneficial bacteria colonies your aquarium needs to convert toxic ammonia into less harmful compounds. It takes patience — typically four to six weeks — but it saves fish lives and sets your tank up for long-term success.

At our shop at 5 Everton Park, we have guided hundreds of customers through the cycling process over the past two decades. This guide walks you through every step, from choosing an ammonia source to confirming the cycle is complete.

What Is Fishless Cycling and Why Does It Matter

In nature, the nitrogen cycle keeps waterways habitable. Fish produce ammonia through waste and respiration. In a mature aquarium, two groups of bacteria handle this toxin. The first group (Nitrosomonas) converts ammonia into nitrite. The second group (Nitrospira) converts nitrite into nitrate, which is far less toxic and removed through water changes.

A brand-new aquarium has none of these bacteria. If you add fish immediately, ammonia builds up with no biological process to remove it. The fish suffer burns to their gills and skin, often dying within days. This is “new tank syndrome” and it remains the number-one killer of aquarium fish worldwide.

Fishless cycling solves this by growing the bacteria before any fish arrive. You add ammonia artificially, let the bacteria colonise the filter media, and only introduce livestock once the cycle is proven to work.

What You Need Before You Start

A fully set-up aquarium — tank, filter running, substrate in place, light on a timer. Plants can be added now (they help the cycle).
Water conditioner — Singapore’s PUB tap water contains chloramine. Treat every water addition with Seachem Prime or a similar dechlorinator.
An ammonia source — see the section below for options.
A liquid test kit — the API Master Test Kit is the standard. You need tests for ammonia, nitrite, nitrate and pH at minimum. Avoid test strips; they are not accurate enough for cycling.
A notebook or phone app — record your readings daily. Tracking the trends is essential.

Choosing Your Ammonia Source

Dr Tim’s Ammonium Chloride

This is the easiest and most precise option. Dr Tim’s produces a liquid ammonium chloride solution specifically designed for fishless cycling. Dosing instructions are on the bottle — typically one drop per litre to reach 2 ppm. Available from most aquascaping shops in Singapore and online.

Pure ammonia (hardware store)

Clear, unscented, surfactant-free ammonia from hardware stores works. Shake the bottle — if it foams, it contains surfactants and must not be used. Finding truly pure ammonia in Singapore can be tricky, so Dr Tim’s is the safer bet.

Fish food method

Drop a pinch of fish food into the tank daily. As it decays it produces ammonia. The downside is imprecise dosing — you cannot control the ammonia concentration easily, and the rotting food can create a messy film. This method works but is the least recommended of the three.

Step-by-Step Fishless Cycling Process

Day 1: Set up and dose

Fill the tank with dechlorinated tap water. Ensure the filter is running and the heater (if used) is set. In Singapore’s climate, ambient temperatures of 28 to 32 degrees Celsius are actually ideal for bacterial growth — warmer water speeds colonisation.

Add your ammonia source until the test kit reads between 2 and 4 ppm. Record the reading. Do not exceed 4 ppm; higher concentrations can stall the cycle.

Days 2 to 14: Test daily and wait

Each day, test ammonia and nitrite. For the first week or two, ammonia will remain high and nitrite will read zero. This is normal. The Nitrosomonas bacteria are colonising but have not yet reached a population large enough to process the ammonia visibly.

Do not add more ammonia during this phase unless the reading drops below 1 ppm. If it does, re-dose to 2 ppm.

Days 14 to 28: The nitrite spike

At some point — usually around week two or three — ammonia readings will start to drop. Simultaneously, nitrite will begin to rise. This is excellent news. It means the first group of bacteria is working.

Nitrite may spike very high, sometimes exceeding what your test kit can measure (the liquid turns a deep purple). This is expected. Continue testing and recording. Do not panic and do not do water changes during this phase unless ammonia or nitrite exceed 5 ppm, which can stall bacteria growth.

Days 28 to 42: Nitrite declines, nitrate appears

The second group of bacteria (Nitrospira) begins converting nitrite to nitrate. You will see nitrite readings slowly decrease while nitrate readings climb. Keep dosing ammonia to 2 ppm whenever ammonia drops to zero, so the bacteria have a continuous food source.

Understanding the Nitrite Spike Phase

The nitrite spike is often the most stressful part of fishless cycling for the aquarist, not because anything is going wrong, but because the numbers look alarming. Nitrite levels of 5 ppm or higher are common and the purple colour on the test kit looks dramatic.

Key points to remember during this phase:

The spike is temporary. It will come down once the Nitrospira colony catches up.
If nitrite stays above 5 ppm for more than a week, do a 50 per cent water change (with dechlorinated water) to bring it down. Extremely high nitrite can inhibit bacterial growth.
Do not stop dosing ammonia. The Nitrosomonas bacteria need food too.
The pH should remain above 7.0. Singapore’s tap water typically sits around 7.0 to 8.0, which is fine. If pH drops below 6.5, the cycle can stall. Add a small amount of crushed coral to the filter to buffer the pH.

When Is the Cycle Complete

The cycle is complete when your tank can process a full dose of ammonia (to 2 ppm) within 24 hours, resulting in:

0 ppm ammonia
0 ppm nitrite
Some measurable nitrate (typically 5–40 ppm)

Test this on two consecutive days to confirm consistency. If both days show zero ammonia and zero nitrite within 24 hours of dosing, your bacteria colony is mature and ready for fish.

Before adding fish, do a large water change (70–80 per cent) with dechlorinated water to bring nitrate levels down below 20 ppm. Then add your first group of fish.

Speeding Up the Cycle

Four to six weeks is the typical timeline, but several methods can shorten it significantly:

Seeded filter media

The single most effective shortcut. If you have a friend with a mature tank, ask for a piece of their filter sponge or a bag of their ceramic media. Place it in your filter. This introduces millions of established bacteria immediately and can cut cycling time to one to two weeks. We offer seeded media at our shop — just ask.

Bottled bacteria starters

Products like Dr Tim’s One and Only, Seachem Stability and API Quick Start contain live bacteria. Results are mixed — some batches work brilliantly, others seem inactive. Use them as a supplement to speed things up, not as a replacement for proper cycling. Even with bacteria starters, test daily and confirm the cycle is complete before adding fish.

Live plants

Aquatic plants absorb ammonia directly, reducing the bacterial workload and providing surface area for bacteria to colonise. Fast-growing stem plants like Hornwort, Water Sprite and floating plants are especially helpful. A heavily planted tank may cycle faster and more smoothly than a bare one.

Higher temperature

Bacteria reproduce faster in warmer water. Singapore’s ambient temperature of 28 to 32 degrees Celsius is already in the ideal range, so you have a natural advantage over hobbyists in cooler climates. No heater needed — just let the room temperature do the work. Read more in our guide on how to cycle an aquarium fast.

Common Mistakes to Avoid

Overdosing ammonia — more than 4 ppm can stall the cycle rather than speed it up. Stick to 2–4 ppm.
Cleaning the filter during cycling — your filter media is where the bacteria live. Do not rinse, replace or disturb it until the cycle is complete.
Using untreated tap water — chloramine in Singapore’s water supply kills the very bacteria you are trying to grow. Always dechlorinate.
Giving up too early — some cycles take six weeks or longer, especially without seeded media. Be patient and keep testing.
Adding fish “just to see” — adding even one fish before the cycle is proven complete puts that fish at serious risk. The whole point of fishless cycling is to avoid this.
Letting ammonia drop to zero for days — if you forget to re-dose and ammonia stays at zero, the bacteria begin to die off. Set a daily reminder on your phone.
Trusting test strips — liquid test kits are more accurate. The difference matters during cycling when precise readings guide your decisions.

Frequently Asked Questions

Can I add plants during fishless cycling?

Absolutely. In fact, adding plants from day one is beneficial. They absorb ammonia, provide bacterial surface area and start growing before fish arrive. Hardy plants like Java fern, Anubias and floating plants tolerate the unstable conditions of a cycling tank well.

My ammonia and nitrite have been stuck at the same levels for two weeks. What is wrong?

A stalled cycle is usually caused by one of three things: pH below 6.5 (add crushed coral), ammonia concentration above 5 ppm (do a partial water change), or chloramine in untreated water (always use dechlorinator). Check all three, correct the issue and the cycle should resume within a few days.

Do I need a heater for fishless cycling in Singapore?

No. Singapore’s year-round temperatures of 28 to 32 degrees Celsius are ideal for nitrifying bacteria. An air-conditioned room that drops below 24 degrees consistently may benefit from a heater, but most HDB and condo setups cycle perfectly at ambient temperature.

How many fish can I add once the cycle is complete?

Start with a small group — perhaps five to six small fish for a 60-litre tank. Adding too many fish at once can overwhelm the newly established bacteria colony. Add more fish gradually over the following weeks, testing water parameters after each addition to ensure the bacteria keep up.

Need Help With Your First Cycle?

Fishless cycling is straightforward but having someone to check your test results and answer questions makes the process far less stressful. Visit us at 5 Everton Park — we stock ammonia sources, test kits and seeded filter media to get your cycle off to a strong start. With over twenty years of experience, we have seen every cycling scenario imaginable and we are always happy to help.

Get in touch or bring your test results to the shop — we will walk you through what comes next.

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