Step by Step Guide to Cycling a New Aquarium


So you have purchased a new aquarium and have taken it home. What will happen next ?

You may have been advised not to introduce too many fish to start with and/or you may have been given some start-up bacteria. Hopefully your local fish shop has also advised you on temperature, P.H. levels, the upcoming and unavoidable nitrogen cycle and feeding amounts required for your fish. If they haven’t done this, then it’s probably a good idea to find a new local fish shop immediately.

What is the Nitrogen Cycle?

You might have heard the terms like “cycling your tank,” “fishless cycling,” “the nitrification process,” or “new tank syndrome” being spoken about by the local fish shop. But, they all refer to the same thing – The Nitrogen Cycle.

So what is it and why is it so important?

All fish release ammonia into the water, which will in turn, kill your fish. Ammonia is released by fish continuously through their gills, but the fish poo (detritus) and leftover fish food are certainly the main reason for a sudden spike in ammonia in the aquarium.

So to counter this.. we rely on a bacterial process called The Nitrogen Cycle. It’s a process where beneficial bacteria becomes established in your gravel, water and especially in the filter media (ie sponge, noodles, bio balls – whatever media your filter might use) allowing ammonia (toxic) to convert to nitrite (toxic), then nitrite to nitrates (not toxic at low levels.)

So basically the beneficial bacteria that will grow in your filter, gravel and water will naturally supplement your fish’s environment by neutralizing their waste.

Most tank cyclings will take between 3 weeks and 6 weeks so let’s talk about what we can do during this period to successfully manage fish.

Nitrogen Cycle of a New Aquarium
Nitrogen Cycle of a New Aquarium

The First 3-6 Weeks of Having a New Aquarium

So there are two basic ways of cycling an aquarium – the fishless way, or with some hardy fish.

Fishless Cycling

It must be said, I am not a fan of fishless cycling. Basically people will add fish food or a piece of fish or prawn itself and basically leave it there to go bad – in turn creating ammonia.

However this method will make horrible odours resinate from the aquarium and the water is sure to take on a milky/cloudy form during the process.

Some shops sell chemicals like pure ammonia or similar too. This would seem to me to be a more sensible way to do this, I still say unnecessary, as if you will read on, it isn’t too difficult to be humane and use fish ie you do not have to sacrifice fish by following some suggestions…

Cycling with Fish

This process does not have to be considered “sacrificing fish” like I have mentioned above – it is more a case of creating the most correct conditions you can to start off, then being diligent with fish selection, food requirements, ensuring correct water parameters and even doing things like adding start up bacteria.

We suggest doing the following:

An air bubbler is a great way to increase oxygen levels.
An air bubbler is a great way to increase oxygen levels.
  • De-chlorinate the water !! Use more than what is suggested.
  • Ensure the filter is working correctly, refer to your manual and ensure it is working by putting your hand in front of the flow.
  • Consider adding an air bubbler to the set up. This will increase oxygen levels for your stock and really help with survival.
  • Purchase a PH test kit and get the PH of the water within the recommended perimeter suggested for your fish. Most tropical fish will happily live around 7.0 (neutral.) Goldfish are most happy at around 7.5 (alkaline.) African Cichlids prefer the water higher still at about 8.0.
  • Purchase “start up bacteria.” There are varying brands (Stress Zyme, Quick Start, STability) some claim to be better than others, they all do the same thing, aquarium companies basically harvest the nitrabatic bacteria and offer it to you in a bottle to add to your aquarium. This will reduce ammonia and nitrite “spikes” and can shorten cycling times of an aquarium to as little as 2.5 to 3 weeks. We recommend a standard daily dose or a dose every 2-3 days for the first 3-6 weeks.
  • Ensure temperature requirements are satisfactory for the fish you have purchased. Tropical fish in most places of the world will require an aquarium heater. Temperature requirements for tropical fish is generally 24C to 28C.
  • Danios are a great choice start up an aquarium using fish
    Danios are a great choice start up an aquarium using fish

    Select the right type of “hardy fish” (danios, various barbs, platies, comet goldfish, nymphs and black widow tetras are good examples of these fish) but refer to your local fish shop on what they might suggest for your particular aquarium. African cichlids are a great choice for a cichlid setup.

  • Selecting the right amount of fish to stock for the first 6 weeks. This is a tricky equation to interpret to a beginner, but we generally have success with suggesting 1 inch of fish per 5 litres of aquarium water for the first 6 weeks or so. So if someone has just bought a 30 litre aquarium, we might suggest up to 6 danios or 6 barbs or 6 black widow tetras at an absolute maximum. Alternatively 2x 5cm comets may also be a good choice.
  • Do not overfeed your fish (ever – but most especially in your aquariums first 6 weeks!) We like to advise people with small fish to just feed each just one to two flakes each, once a day during the Nitrogen Cycle period.

Remember there is no bacteria in the aquarium yet to break down the detritus! This is probably the most important piece of advise in this entire article, if you overfeed your fish you will most certainly kill fish. Ensure food is completely consumed by fish within 30 seconds, it will seem to you like it is not enough, but it is.