🇩🇪 DE
New & free · AI-powered

Aquarium cycling
guided intelligently

The first assistant that understands your water readings, automatically detects the nitrogen cycle stage, and tells you whether nitrite, ammonia and nitrate are on the right track.

Start for free → Already registered

Free · 5 AI analyses included · no credit card required

The nitrogen cycle explained

What happens during cycling?

Before fish can move into a new aquarium, a bacteria colony needs to build up that breaks down ammonia (NH3) via nitrite (NO2) into harmless nitrate (NO3). This process is called nitrification and typically takes 4–8 weeks.

1
Stage 1 – Ammonia rising (week 1–2)

Ammonia/ammonium rises. Nitrosomonas bacteria start colonizing the filter media. No water changes – ammonia is food for the bacteria.

2
Stage 2 – Nitrite rising (week 2–4)

Nitrite spikes sharply – acutely toxic to fish. Ammonia starts to drop. Nitrobacter bacteria colonize and break nitrite down into nitrate.

3
Stage 3 – Nitrite dropping (week 4–6)

Nitrite drops to 0. Nitrate becomes measurable. The finish line is in sight.

✓
Stable – fish can move in

Ammonia < 0.05 mg/l, nitrite < 0.1 mg/l and nitrate measurable – no earlier than 4–6 weeks in. The assistant shows you the trend and gives an assessment. The final decision is yours.

What the assistant can do

Unique in fishkeeping

🧪

Automatic phase detection

You log your readings – the assistant recognizes on its own which stage your tank is in and what to expect next.

🤖

AI trend analysis – free

Every few readings, an AI analyzes your trends and gives you concrete, personalized tips. 5 analyses included in the free plan.

🚨

Real-time danger alerts

If ammonia or nitrite reach critical levels, you get an instant alert with concrete action steps.

📈

Progress & ETA

Progress bar and estimated time remaining based on your actual readings.

🐠

Built-in stocking planning

From day 7, the assistant shows fish suggestions suited to your tank type – you can add favorites straight to your wishlist.

🏆

Cycling certificate

Once cycling is complete, you get a certificate with all readings as proof.

In 3 steps

How to get started

1
Set up your tank and start the wizard

Enter substrate, planting and cycling method. The wizard automatically adjusts tips and fertilizer recommendations.

2
Log readings regularly

Ammonia, nitrite, nitrate, pH – measure and log every 1–2 days. Optionally add a photo for a visual log.

3
Assistant recognizes the right moment

Once all parameters are stable and at least 4–6 weeks have passed, the assistant gives you an assessment. The final decision is always yours – with a certificate as your log.

Why a forum thread isn't enough

With assistant vs. on your own

Without an assistant
✗Guessing when the stage ends
✗No alert for dangerous nitrite levels
✗Conflicting forum advice
✗No measurement log
✗Added fish too early?
With Aqualizer
✓Automatic phase detection
✓Real-time alerts for danger
✓Personalized AI tips
✓Visual measurement log
✓Trend assessment as a decision aid
Frequently asked questions

FAQ about aquarium cycling

How long does aquarium cycling take?
Typically 4–8 weeks. With bacteria starters (e.g. JBL Denitrol), the duration can be reduced to 2–3 weeks. In heavily planted tanks with CO2 (silent cycling), it can even take under 2 weeks, because plants absorb nitrite directly.
When is nitrite (NO2) dangerous in an aquarium?
Problematic from 0.1 mg/l for sensitive species (shrimp, tetras), acutely toxic to most fish from 0.5 mg/l. A spike of 2–10 mg/l during cycling is normal – that's why no animals should be in the tank during this period.
What is fishless cycling?
Cycling a tank without fish – ammonia is provided daily via a pinch of fish food, soil, or targeted ammonia solution. It's animal-welfare friendly and recommended as the "standard (no animals)" method.
When can I add fish after cycling?
Only once ammonia is consistently below 0.05 mg/l, nitrite is consistently below 0.1 mg/l, and nitrate is measurable (at least 5 mg/l) – and no earlier than 4–6 weeks in, even if readings look good sooner. Our assistant shows you the trend and gives an assessment, but the final decision is yours.
Why does my nitrite stay elevated for so long?
Common causes: (1) temperature below 24°C inhibits Nitrobacter, (2) pH below 6.5 blocks nitrification, (3) KH below 3 °dH causes pH to crash, (4) too many water changes wash away ammonia as a food source. The nitrite spike can last 2–4 weeks.
Which water tests do I need during cycling?
Required: an ammonia/ammonium test and a nitrite test. Recommended: a nitrate test, pH test and KH test. Our wizard explains exactly which tests you need and links to suitable products.
🐠

Start your first cycling

Free, no credit card. With 5 AI analyses included. And the only assistant so far that truly understands what's happening in your tank.

Register for free →