How to Cycle a Saltwater Aquarium

The biological process a new saltwater aquarium goes through is called the nitrogen cycle.
The biological process a new saltwater aquarium goes through is called the nitrogen cycle. (Image: Marine Fish image by Lucid_Exposure from

A new salt water aquarium goes through a biological cycling process before stabilizing. The length of this process, which varies from aquarium to aquarium, is termed the nitrogen cycle. Heterotrophic bacteria begin this process by breaking down complex proteins into inorganic compounds. Ammonia, which is toxic to fishes and invertebrate animals, is formed. Two types of autotrophic bacteria are then responsible for the biological oxidation of ammonia. Nitrosomonas bacteria convert ammonia to nitrite (NO2) and Nitrobacter bacteria convert the nitrite to nitrate (NO3). Nitrates are further reduced through water changes, through the process of denitrification, or by the addition of commercial products that absorb them. The entire process must be completed in order for the environment to be able to support live rock, fish and other aquatic life.

Things You'll Need

  • Sea water aquarium, 60-gallon capacity
  • Small bottle of chlorine neutralizer
  • 17 lbs. of synthetic aquarium salt
  • 150-watt aquarium heater
  • Submersible pump
  • Aquarium filter
  • 20 lbs. of new aragonite substrate
  • 10-gallon plastic bucket
  • Garden tap
  • Long-handled net
  • Long plastic aquarium tongs
  • 2 lbs. of aragonite substrate from an established aquarium
  • 30 lbs.of live rock
  • Three hermit crabs
  • Meaty seafood
  • Ammonia test kit
  • Nitrite test kit
  • Nitrate test kit

Fill the 60-gallon aquarium with tap water and add 5 oz of chlorine neutralizer.

Add the synthetic salt to the aquarium. Stir vigorously as you add the salt.

Place the 150-watt heater and submersible pump into the aquarium and plug both into a wall power source. Set the thermostat on the aquarium heater for 79 degrees Fahrenheit. Allow the aquarium water to circulate and warm up for 24 hours.

Connect your filters.

Place 5 lbs. of new aragonite sand into the 10-gallon bucket and rinse it under a garden tap until all the dust and debris has been washed away. Gently tip the water from the bucket, into a drain. Be careful not to lose gravel in the process.

Fill a long-handled net with the recently cleaned aragonite and place the net into the aquarium. Hold the net just above the aquarium floor and using the long plastic aquarium tongs, take hold of the bottom of the net and gently tip the gravel out.

Continue to rinse and add the aragonite until all the sand has been cleaned and placed in the aquarium.

Use the aquarium net to place the 2 lbs. of aragonite from an established and cycled tank into the aquarium. Spread this cycled aragonite over as much of the new sand as possible. Beneficial bacteria that are already colonizing the cycled aragonite will establish on the new sand.

Place the live rock into the aquarium. The rock itself is not alive, but is covered with living invertebrate life, such as sponges and higher algae and beneficial bacteria.

Add the hermit crabs to the aquarium after 48 hours. Feed the hermit crabs lightly on tiny pieces of meaty seafood, such as calamari or prawns.

Test for the presence of ammonia on a daily basis.

Test for the presence of nitrite (NO2) as soon as the level of ammonia peaks and begins to drop to zero.

Add the first fish after the nitrite reading has dropped to zero.

Only add one or two fish at a time, as the established bacteria colonies will need to grow in order to process the additional metabolic waste.

Perform weekly 10 percent water changes in order to dilute the nitrate (NO3).

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