Saltwater Livestock

So, you’ve gone out and got yourself a tank, the pumps, an RO/Di unit, some salt, maybe a skimmer and reactor, everything is ready for your first fish… or is it?

The only thing you need to know to know if you can safely add your first fish, is that your Nitrogen cycle has complete. As long as it is complete, your tank should be ready for your first hardy fish. But how do you cycle your tank and how do you know if your cycle is complete?

What is the Nitrogen Cycle?

The Nitrogen cycle in simple terms is all about bacteria. Your fish produce ammonia, it predominantly comes from their waste. Rotting fish food will also cause ammonia, along with a couple of other natural sources within your tank. Ammonia is very toxic to your fish.

Ammonia gets eaten up by bacteria which produces Nitrite. This bacteria will populate your tank naturally. Nitrite is also toxic to your livestock, but it is not quite as bad as ammonia.

Along comes another form of bacteria which eats up the Nitrite, this then produces Nitrate. Nitrate is far less toxic to your livestock. Nitrate can be exported via water changes, carbon dosing and via a refugium with something like Chaeto growing in it.

Nitrogen Cycle Example Graph
Nitrogen Cycle Example Graph

These bacteria will live on hard surfaces, so things like your glass, filter media and more importantly your rock. In the saltwater hobby we use what is referred to as “live rock”, this rock is very porous and has a greater surface area for your bacteria to populate. It is the bacteria living on your rock that gives us the term “live rock”. You can use alternative ceramic media and “false live rock” if you don’t fancy pulling rock out of the ocean (which I personally don’t!).

You can use dry live rock or ceramic media and then seed your tank with the required bacteria via live sand, a handful of sand from an established tank, bottled bacteria or a smaller piece of live rock from an established system.

Once you have seeded your tank, as long as you have an ammonia source you just have to wait for your bacteria to multiply and complete your cycle.

How do I start my Nitrogen Cycle?

There are a few different options you can look into to start your cycle.

Prawn to start the Nitrogen Cycle
Prawn to start the Nitrogen Cycle
  1. Ghost feeding your tank. You can add a small pinch of fish food each day to your tank and let it rot. By allowing it to rot you will allow ammonia to begin appearing in your tank. You should keep ghost feeding your tank until you are ready to put fish in your tank to ensure there is a constant food source for your bacteria.
  2. A rotting prawn/shrimp. By placing a prawn (in a mesh bag) into your tank and just letting it rot away you will start your cycle. You should leave the prawn in the tank until your cycle is complete and you are ready for fish. One of the big advantages of cycling your tank with this method is you don’t have to remember to feed your tank (that’s without mentioning the waste of fish food!)
  3. Bottled ammonia. This method works the same way as the ghost feeding, a few drops of ammonia each day will allow the cycle to start. Please ensure your ammonia is safe for aquarium use.
  4. Bottled bacteria. A popular choice amongst new aquarists is to buy ready made bacteria in a bottle. This is by far the fastest way to cycle a tank as your water is often ready for fish within 24 hours. (PLEASE READ SPECIFIC INSTRUCTIONS ON THE BOTTLE, don’t take 24 hours as a given as each manufacturer will have their own guidelines)

I personally chose to cycle my tank with the prawn method. You can read more about my experience with it here >>>

How do I know my Nitrogen Cycle is complete?

Your Nitrogen Cycle is complete once your water testing results show the following:

  • Ammonia = 0
  • Nitrite = 0
  • Nitrate levels will vary, some people will have a reading of 10 others will have 50+. Anything below 20 is generally considered safe, if you have higher readings, do a water change to bring the numbers down.

Recommended test kits include RedSea & Salifert. It is generally regarded within the hobby that the API test kit is not accurate enough.

The cycle can take anywhere from 2 to 8 weeks+ and usually it is just a case of waiting it out and doing your water tests. When doing your test your are looking for a spike in ammonia, which will be followed by a spike in Nitrite. Both of these levels will drop to 0 and you will be left with just Nitrates.

My Cycle is complete, what next?

Dartfish Goby
Dartfish Goby

Congratulations! Your tank is now fish ready. You can begin stocking your tank slowly. Don’t rush in and put loads of fish in at one time as you will likely cause an ammonia spike and a mini cycle.

This is assuming you are up to temperature in your tank and have the correct salinity level.

You can read my guide on choosing your first fish here >>>