Should I bother cycling a planted tank before planting? Introducing the dark start.

Tank cycling is important for a few reasons.

Diatoms and green dust algae are common in new setups. It is so common that many experienced people think it is an inevitable stage that all tanks must go through. However, both of these algae stages are greatly minimised or absent if the tank is allowed to pre-cycle and mature beforehand. Especially for beginners who find algae difficult to deal with, avoiding the problem from the start is a wise move.

What makes a mature tank so much more stable than a fresh installation is the microbial population that develops in a tank system over time. Microbes and decomposers break down and consume organic waste. A biologically mature system is one in which there is sufficient microbial life to rapidly break down harmful organic pollutants into benign substances. This creates a more favourable environment for both animals and plants. The faster waste is broken down, the fewer triggers there are for algae to spawn. Many microbes also consume algae directly. 

Cycling a tank before planting reduces both algae and plant melting occurring.

For tanks that use higher levels of light, its easy for plants in a new tank to be quickly smothered with algae if the biological environment is not matured.  

Ammonia is great as plant food ?

Ammonia is an excellent source of nitrogen for plants, which generally use less energy to synthesise nitrogen from ammonia than from nitrates. Ammonia binds to clays and organic matter in the substrate, and plants that can obtain nitrogen from an ammonia-rich substrate grow better and more robustly.

However, ammonia in the water column can exacerbate algae problems and affect delicate plant species. Allowing the tank to cycle and removing excess ammonia before planting will provide a more stable environment for the plants to settle into.

Bucephalandra are undemanding plants, but require a stable, clean, well filtered environment to do well long term. This easy plant often melts in new setups.

Reduced toxicity of ammonia below pH 7?

In biological systems, ammonia can occur in two forms - ionised (NH4+) and unionised (NH3). The amount of ammonia present in either form is largely dependent on the pH range of the aquarium. Ionised ammonia (NH4+) is much less toxic. Therefore, the toxicity of ammonia is greatly reduced in lower pH environments as most of the ammonia present will be in the form of ionised ammonium (NH4+). In aquasoil tanks where high levels of ammonia are emitted, one can avoid most of the disadvantages of elevated ammonia due to the strong buffering capacity of the soil which lowers the pH below 7.

Tank cycling The old way

The old method of cycling a planted tank was to add a light load of hardy fish, which produce organic waste and ammonia, and then leave the tank to build up the bacteria naturally over time. This could take many weeks as more and more animals were slowly added. Seeding the tank with seasoned filter media or mulch from a previous set-up are other ways to start the cycle. Depending on how it's done, this process can be hard on the animals.

Today's fish-less cycling with plants

Nowadays, fish-less cycling with plants is the rage. This involves adding liquid ammonia regularly into a new tank; fully setup except for livestock or plants, to grow the bacteria colonies. Follow these 3 steps:

1. A dose of 2ppm ammonia is added, then the water is tested after a few days (it takes about 3 days from a cold start to see any change at all). When the ammonia levels start to drop, you would see a build-up of nitrite. The first step of the ammonia oxidation cycle has started (but not necessarily completed).

2. Additional ammonia is then added each day to feed the bacteria (enough to bring the levels back up to around 2ppm). After many more days the nitrite levels would fall and you can then measure the rise in nitrate levels as the bacteria that convert nitrite to nitrate have colonised. This will take longer than step 1 because the bacteria responsible for converting nitrite to nitrate are slower to populate.

3. Eventually, even with the addition of ammonia, nitrites and ammonia would be measured at 0 after 6 hours, while nitrates would accumulate. The ammonia cycling process for the tank is now complete. The whole process can take 4-6 weeks depending on the tank parameters.

Typically, we would change 80% of the tank water to reduce nitrates before adding animals. Adding starter bacterial cultures at step 1 speeds up the process considerably. Bacterial products work, but many are sensitive to temperature. Depending on how they are transported and stored, cultures can be DOA (dead on arrival). This is the main risk/disadvantage of bacterial products.

Cycling with aquasoils (Dark start):

1. If you are not using starter bacteria products, it is a good idea to add mulm or used filter media to get the cycle started. Without the use of starter bacteria products, a full tank cycle can take up to a month or more. The lowered pH of the tank water due to the buffering capacity of Aquasoil reduces ammonia toxicity as most of the ammonia is present in the less toxic ammonium (NH4+) format at low pH (below 7). This allows hardy plants to be planted and grown at early stages where ammonia levels are detectable. However, more sensitive plants such as Utricularia gramminifolia, and tissue culture plants in general, should not be planted until the tank has been cycled - they melt easily in fresh soil.

2. With the use of starter bacteria products, cycling time can be shortened to a week plus. After filling the tank, we recommend letting the tank soak for a couple of days without running the filter. On the second or third day, do a 100% water change then start running the filter. This removes organic debris, dust and sugars released from the woods and prevent the filter from taking up a lot of debris at the start. After starting the filter, dose the starter bacteria culture into the filter intake. We would increase the KH to 3dKH and add a few pieces of limestone (about 200 grams of Seiryu per 100 litres) temporarily to the tank to prevent tank water from becoming too acidic if the water is super soft.

3. Wait 4 days and take ammonia and nitrate readings. If there are nitrate readings, it means that the cycling has started. However, due to the tremendous amount of ammonia the aquasoil releases, chances are ammonia readings will still be high. Do a 90% water change and dose another dose of starter bacteria culture.

4. Wait a day and take ammonia/nitrate readings. If the ammonia reading is 0 and the nitrate reading is positive, the tank has cycled. However, if soil loading is high, the ammonia reading may still be positive as the soil releases a lot of ammonia, in which case wait a few days and repeat step 3. Due to the reduced toxicity of ammonia below pH 7, which is generally the case in aquasoil tanks, standard, non-delicate plants can be planted as long as ammonia levels are low (below 0.5ppm or so). However, for sensitive animals such as shrimp, it is better to wait until the tank is fully cycled.

In the setup videos on Youtube, folks seem to plant immediately in fresh aquasoil ?

The type of plants and aquasoil used is very important. Hardier plants can be used in a fresh set up without too much of a downside.

What you also don't see is the daily water changes, replacement of melted plants and algae cleaning that goes on behind the scenes. Hardy species planted directly into fresh soil will generally recover, even if they take the initial hit from the uncycled tank. However, for many beginners who do not have good control of their CO2 and other growth parameters, this could result in the loss of entire batches of plants.

For planting immediately without cycling follow this guide instead.