Tank Cycling

API freshwater test results

What is cycling?

Simply put, cycling an aquarium means building up a large enough colony of beneficial bacteria in your filter to safely consume your animals’ waste before it can cause health/stress issues.

In technical terms, your fish/livestock will produce ammonia (NH4) as waste and it is poisonous for the fish/livestock. To prevent a build up of ammonia you should allow certain beneficial bacteria, called Nitrosomonas, to grow a healthy population which will consume the ammonia and output nitrite (NO2).

However, whilst nitrite is less dangerous, it is still poisonous to fish and so another type of bacteria is required to finish the job; that would be Nitrospira. Nitrospira consume the nitrite (NO2) and break it down into the much less harmful nitrate (NO3) which can then be more easily consumed by plants etc.

These beneficial bacteria colonies grow mostly in your filter and on the porous surfaces/materials with high surface area such as filter sponge, lava rock, ceramic bio rings, etc.

The cycling process is complete once there is 0ppm of ammonia and nitrite, and 2pmm of ammonia can be converted in 24 hours.

You must be patient as the cycling process can take around 4-6 weeks to complete. You can speed up the cycling time by using ready-made bacteria products or “seeding” your new filter with media from an already established filter.

Filter types

Typically filters will serve two purposes: biological and mechanical.

Biological filtration will typically be an amount of media with high surface area such as ceramic bio rings, bio balls, sponge, lava rock, etc. This is where the vast majority of the beneficial bacteria colonies will live and grow as the continuous flow of tank water will allow them to thrive.

Mechanical filtration captures debris of various different sizes to keep your water looking clear and free of floating particles. Filter floss and sponges are the most common types of mechanical filtration media. Note that sponge serves as both a biological and a mechanical filter component.

However, another of type of filtration available is chemical filtration. This is the addition of an element which will change the water chemistry in a desired way, such as activated carbon/charcoal. Activated carbon will trap chlorine/chloramine, tannins (the cause of dark water), any medications you've added to the water.

The activated carbon works by trapping the elements in tiny pores on its surface, and as a result will only work efficiently for a limited amount of time depending on how much trapping it does. To maximize its efficiency you should always place chemical filtration after mechanical filtration (i.e. behind filter floss) to prevent larger debris from blocking the trapping pores.

Fishless Cycling


  • Source of ammonia
  • Aquarium water test kit

The fishless cycling process is the recommended way as no stress is put on animals and it's easier to manage.

To avoid placing any stress on live animals, we need to introduce a source of ammonia such as a raw prawn from a supermarket, or some pure ammonia solution such as Dr Tim's Ammonium Chloride. Be careful to ensure the ammonia solution is pure and does not contain any perfume or other undesirable ingredients.

Introduce 2-4ppm of ammonia by adding your ammonia source and testing until you reach the desired range. Once there you should test your water for ammonia and nitrite every few (1-3) days and record the results. Once the ammonia has been consumed and converted into nitrite, add more ammonia to the 2-4ppm range again. After a few days/weeks you should then start to see the nitrite level decline and the nitrate level climb, signalling the cycle is nearly complete.

Once your cycle is complete (2ppm of ammonia can be consumed in 24 hours), perform a water change to remove some of the excess nitrates. Afterwards you can add your livestock of choice.

Fish-in Cycling


  • Seachem Prime / other water dechlorinator product
  • Aquarium water test kit

The method known as fish-in cycling is discouraged because it can place large amounts of stress on the fish, leading to health problems or death.

If you've already added your fish to a new (uncycled) tank, or your cycle crashed and you can't return your fish then you'll have to use this method.

Carefully monitor your water's ammonia, nitrite, and nitrate levels daily and add your dechlorinator product of choice (e.g. Seachem Prime) when ammonia/nitrite is detected. Perform water changes every few days to avoid overdosing on the chemicals and ensure that nitrates do not build up either.

Other ways to improve cycling


There are multiple benefits to adding plants to a shrimp tank such as increased surface area for biofilm and algae to grow, absorbing excess ammonia/nitrates, and giving the shrimp places to hide after molting.

One thing to be careful of is that you might need to dose aquatic plant fertilizer into the tank depending on how demanding the plants are. Some of these fertilizers might contain copper, which can be very toxic to shrimp so ensure that the amount is miniscule or non-existent to be safe.

Walstad method

The Walstad method is a process of setting up a planted tank which involves putting soil at the bottom of the tank and then capping it with gravel. This allows the plants to access all of the nutrients they need via their root systems and you won't need to worry about dosing fertilizers into the water column.

Bacteria in a bottle

If you don't have access to seeded filter media (i.e. a sponge taken from an already cycled tank) then there are some products you can buy that aim to speed up the bacteria population growth.

Some examples of this are API Quick Start, Tetra SafeStart, and Seachem Stability.