The Aquarium Cycle

The most important step in setting up an aquarium is knowing about the aquarium cycle to make sure that the nitrogen cycle is in full swing before you add your fish

 You need to cycle an aquarium to get the nitrogen cycle working at the start.

When you first set up your aquarium it will lack any of the nitrifying bacteria that are essential to maintaining water quality and it is only through knowing how to cycle an aquarium that you can get the balance right.  It will take time but is probably the most important thing that you ca do towards successful aquarium keeping.

The Aquarium cycle is simply the process of setting up the aquarium so that it develops the nitrifying bacteria in the substrate and the filter and there are two main ways of doing this.........with fish or without fish.

The Aquarium Cycle with Fish

I am assuming that at this stage you have already set up your tank, have it planted and have dealt with any chlorine in the water.  Chlorine and bacteria do not mix and your tank will not cycle with chlorine in it.

You need to choose two or three starter fish and add these to your newly set up tank. Start feeding them but take care not to over feed them as this will cause problems.  If in doubt about the amount of food watch them eating to make sure that they are eating all the food that you put in the tank.

After a day or two you need to test the water for an increase in Ammonia.  It may be a few days until the Ammonia levels have increased greatly but don't let them get too high.  Under 0.25 is fine but anything over that and you will need to do a partial water change to bring the Ammonia levels back down.

As the biological filter starts you will see nitrite levels increasing and ammonia levels decreasing as the Nitrosomonas(bacteria) start to grow and do their work.  Eventually you will see nitrate levels start to rise as the  Nitrospira bacteria start to do their job.  Once your Ammonia and Nitrite levels are zero you have established a biological filter and are ready to start adding extra fish.

But always a few at a time so as not to overwhelm the biological filter.

The Fishless Aquarium Cycle

There is a growing movement amongst aquarists to cycle new aquariums using a fishless aquarium cycle. 

Fish that are used for cycling an aquarium will experience peaks in Ammonia and Nitrites and will suffer stress as a result.  If you are confident that you will be able to monitor Ammonia and Nitrite levels on a regular basis and react accordingly, then you reduce the levels of stress for the fish and may feel confident that the fish will not suffer.

If you have any doubts and would like to cycle your tank without using starter fish then read on....

The aquarium cycle is exactly the same as above but without the fish.  Rather than relying on the fish waste to add ammonia you will be adding it through other means.

What you can do to add some ammonia and start the process off is to add small amounts of  fish food.  This food will sink to the bottom of the tank and start to decay causing ammonia to be formed.  This in turn will cause the nitrifying bacteria production that is needed.  The whole process can take four to six weeks but don't be tempted to take any short cuts as adding fish at this stage will simply cause ammonia and nitrite spikes and the distress to the fish that you were trying to avoid.

Another method is to add a frozen prawn in a nylon net to the tank.  As the prawn decays it will add ammonia and start the aquarium cycle.  For someone who is trying to avoid fish suffering, it does seem bizarre to use a dead fish!!

The third method is to use household ammonia.  Make sure that it is unscented and then add Ammonia to the tank until you get a reading of about 4 ppm.  This gives the conditions for the start of the aquarium cycle.  It is then a matter of monitoring the Ammonia, Nitrite and Nitrate readings, topping up the ammonia occasionally.  Once the Ammonia level returns to zero within about twelve hours you know that you have enough nitrifying bacteria to support your fish population.

Remember - Any kind of medication added to the tank can destroy the biological filter.  If this happens the tank needs to be cycled all over again.

Tip - When you have moved on to your second tank, you can short circuit the delay by adding some of your old substrate to your new tank.  This will already contain the bacteria and will 'seed' the tank to speed up the process.