When is the marine aquarium ready?

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When is your Marine Aquarium fully run-in?

After starting up your marine aquarium with live (or dead) rock and starting the nitrogen cycle, the inevitable question arises: when will my aquarium be ready for its first inhabitants?

An aquarium is only properly run-in when the biological filter is functioning stably and waste products are being efficiently converted. Below, we explain how to recognize this and what to look for.

1. Check water values

The most important way to determine if your tank is broken in is by testing the water parameters. This primarily involves measuring:

• Ammonia (NH₃): should be at 0 ppm
• Nitrite (NO₂): should be at 0 ppm
• Nitrate (NO₃): must be demonstrably present (usually between 5–30 ppm)

If you first see a peak in ammonia, followed by a peak in nitrite, and then a rise in nitrate, then the nitrogen cycle has been completed successfully.

2. Stability over several days

A one-time measurement isn't enough. Test over several days. As long as ammonia and nitrite remain at 0 and nitrate remains slightly present, you can assume the system is stable.

3. Visual signs of maturation

Besides testing, you can also observe visual signals:

• Light deposits of brown algae (diatoms) on the sand or stone
• Possible incipient algae growth (such as green deposits)
• Emergence of micro-life on living rock (e.g. copepods or sponges)

This stage is part of healthy maturation and is no reason to panic.

4. First residents: start the clean-up crew

Once your water parameters are stable, the aquarium is ready for the first life forms. Start cautiously:

• Cleaning animals such as hermit crabs , snails or shrimps
• Preferably no fish or sensitive corals yet

Observe carefully whether the values remain stable after adding the first animals.

Be careful when starting up with dead stone

If you only used dead stone, the maturation process may take longer. You will often:

• Have to wait longer for nitrate formation
• Benefit more from additional bacterial starters or additives such as live sand products

Summary

You can recognise a well-established marine aquarium by:

• Ammonia = 0
• Nitrite = 0
• Nitrate = present
• Stability over several days
• Cautious first life forms can be added

Take your time: a well-run aquarium is the key to long-term success!