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Should I bother cycling a planted tank before planting?

October 02, 2022 6 min read

Should I bother cycling a planted tank before planting?

Tank cycling is important for 2 main reasons.

1. Ammonia melts delicate plants (such as plants that come in tissue culture format) and is harmful to livestock. This is more important for aquasoil tanks that use ammonia rich aquasoils, where initial ammonia levels can be significant. 

2. Having matured microbial community in the tank allows faster processing of organic waste pollutants. This maturation process reduces incidence of triggering algae. This take a long time without seed material (mulm/mix of old substrate from previous tanks etc). Avoid triggering algae in a new setup allows plants to settle in more smoothly. This is especially applicable for high light setups.

Cycling before planting reduces algae triggers, and creates a better, more stable environment for sensitive plants & livestock. Diatoms and green dust algae are common in new setups; so common that many experienced folks think that it is an inevitable stage that all tanks have to pass through. However, both these algae stages are greatly minimized or absent if tank is allowed to pre-cycle and mature beforehand. Especially for beginners that have a hard time handling algae, avoid the issue to start with is a smart move.

If you are using relative easy/hardy plants and non-ammonia rich substrates, then planting without pre-cycling is fine.

For tanks that use higher levels of light, its easy for plants in a new tank to be quickly smothered with algae if ammonia levels are elevated.  

Ammonia is great as plant food ?

Ammonia is a great source of Nitrogen for plants; which generally use less energy to synthesise Nitrogen from ammonia than from say Nitrates. However, since ammonia is toxic, plants cannot store the compound directly in their tissue, and have to reduce the ammonia to Nitrate before it can be stored. This means that plants can only use Ammonia effectively for growth at the point of growth - having excess is not conducive and plants will not be able to uptake large amounts of it.

The downside of having ammonia in the water column is that it is toxic to both fish and plants. This is a key reason why delicate plants such as Utricularia graminifolia melt when planted freshly in new setups. The other hardy plant that melt in new setups often is Bucephalandra. Both these species are much better off in matured tanks.

Besides its toxicity, ammonia is also a great trigger for algae. This is especially an issue for tanks with higher light levels - where the tank can become quickly covered in diatoms and green dust/green spot algae making it difficult for plants to adapt to the new environment as algae start covering their leaves.

The trade off of instability due to ammonia spikes is not worth the marginal boost in plant growth that ammonia would give. In newly planted tanks, Nitrogen uptake is slow as plants that have not settled into the new environment would not be growing at maximum growth speed yet. Most of the ammonia present would end up being oxidized to nitrates over time.

Having ammonia in the substrate rather than the water column allows us to boost growth without having an additional algae trigger in the water column.

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 due ammonia and other organic contaminants.

Tank cycling The old way

​The old method of cycling a planted tank was to add a light fish load of hardy fish, which then produce organic waste and ammonia; the tank was then left to build up the bacteria naturally over time. This can take many weeks, as more and more livestock was added slowly. Seeding the tank with seasoned filter media or mulm from the substrate of a previous setup are additional ways to kick start the cycling process. Depending on how it's done, this process can be tough on livestock. In acidic tanks (pH <7), ammonia toxicity is alleviated as most of the ammonia is in the NH4+ (ammonium) format due to low pH environment.

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 of ammonia is added, then the water is tested after a couple of days (takes about 3 days or so from a cold start to even see levels change). When ammonia levels start to decline, one would start seeing a build-up of nitrite. The first step of the ammonia oxidation cycle is started (but not necessarily completed).
  2. Additional ammonia is then added every day to feed the bacteria (add enough to raise levels back to around 2ppm). After many more days, nitrite levels would fall, and one can then measure nitrate levels rising as the bacteria converting nitrite to nitrate has populated. This takes longer than step 1 as the bacteria responsible for nitrite conversion to nitrate populates more slowly.
  3. Eventually, even with additions of ammonia, nitrites and ammonia would measure at 0 after a 6hr period, while nitrates accumulate. The ammonia cycling process for the tank is now complete. The entire process can take 4-6 weeks depending on tank parameters.

Typically, we would change 80% of tank water to reduce nitrates before adding livestock. Adding starter bacteria cultures at step 1 greatly speeds up the process. Bacteria products work, but many are sensitive to temperature. Depending on how it is transported and stored, cultures could be DOA (dead on arrrival). That is the main risk/downside with bacteria products.

Cycling with aquasoils:

  1. If you do not use starter bacteria products, it is a good idea to add mulm or used filter media to kickstart the cycle. Without the use of starter bacteria products, full cycling of the tank can take up to a month or more. The lowered pH of the tank water due to the buffering capacity of aquasoil reduce ammonia toxicity as most of the ammonia exists as less toxic ammonium(NH4+) format in low pH (below 7). This allows hardy plants to be planted and grown even in early stages where ammonia levels are detectable. However, more sensitive plants, such as Utricularia gramminifolia, and tissue culture plants in general, should only be planted after the tank is 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 ammonia reads 0 and nitrates reading is positive, tank has cycled. However, if soil load is high, ammonia reading can still be positive as the soil releases a lot of ammonia, in that case, wait a couple of days and repeat step 3. Due to reduced ammonia toxicity below pH 7, which is what will generally happen in aquasoil tanks, planting of standard, non-delicate plants can happen as long as ammonia readings are low (below 0.5ppm or so). However, for sensitive livestock such as shrimps it is better to wait till the tank has fully cycled.

Cycling Process Chart 1Cycling process chart 2

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

The type of aquasoil used matters a lot. Aquasoils with little to no ammonia release doesn't have the same impact as ammonia rich aquasoils. 

What you also do not see is the daily water changes, replacing of melted plants and cleaning of algae behind the scenes. Hardy species that are planted straight into fresh soil generally recover even if they take the initial hit from ammonia. However, for many beginners that do not have good control of their CO2 and other growth parameters, it could result in losing entire batches of plants.