Dark Start is a way of starting a planted aquarium in which the tank runs for the first few weeks without light, plants, CO₂ or fertilisation. The purpose is to let the active substrate pass through its most intensive initial phase while biological filtration develops before planting.
Fresh active substrate can release elevated amounts of ammonia and other substances during the first weeks. Regular water changes gradually remove them and give the filter time to establish a more stable bacterial population. After planting, the aquarium therefore starts from a much calmer position. Dark Start is not a guarantee of an algae-free aquarium, but when carried out correctly it can significantly reduce the risk of problems during the first weeks.
In practice I allow approximately 5–6 weeks. I treat this as a working framework, not a fixed calendar. The exact course depends on the substrate, the amount of hardscape, filtration and measured water values.
Dark cycling phase Weeks 1–6
In the first phase I build the finished hardscape, fill the aquarium and let the filtration run. Plants come later.
Hardscape and substrate
In my tanks I use Yokuchi Ganban Power Base as the lower nutrient layer and Yokuchi Jiban Soil as the main active substrate. Jiban Powder can be used for finer work in the foreground. The same Dark Start principle can be used with other active substrates, but their initial behaviour may differ.
- Finish the composition of stones, wood and any decorative sand.
- Do not add plants or mosses at this stage.
- Keep in mind that small changes to the hardscape become harder to make after several weeks.
Filling and filtration
- Fill the aquarium slowly over a sheet or plastic bag so the substrate is not disturbed.
- Start the filter and set good water circulation without unnecessarily stirring the substrate.
- Add starter nitrifying bacteria according to the manufacturer’s instructions.
- Keep the light off. The aquarium does not need an opaque cover — the key point is simply not to light it.
- I do not use CO₂ or fertilisers at this stage.
Water-change schedule
With active substrate, regular water changes are more important to me during the first weeks than trying to leave the aquarium “untouched”. I use the following regime as a practical starting point:
| Period | Frequency | Volume |
|---|---|---|
| Week 1 | 3–4× per week | 50% |
| Weeks 2 and 3 | 2× per week | 50% |
| Weeks 4–6 | 1× per week | 50% |
If the aquarium will run long-term on reverse-osmosis water, I use RO water from the first fill. For a tank planned for tap water, you can stay with tap water or switch to RO gradually. After each water change, an appropriate dose of nitrifying bacteria can be added.
Time alone is not the only check. Before moving on to planting, it is sensible to verify that NH₃/NH₄ and NO₂ remain at zero and that the tank does not show another significant rise after water changes.
Planting and start-up End of Dark Start
Large water change
Before planting I drain approximately 80–90% of the water. This removes as much as possible of the residual substances released during cycling and gives comfortable access to the hardscape.
This is also the last convenient moment for small corrections to stones, wood or decorative sand.
Mosses: two options
I attach mosses with Yokuchi Plant Glue, or secure them with fishing line or thread. I then continue directly with planting the remaining plants.
I finely chop the moss or briefly blend it with a little clean water and brush it onto damp stones or wood. This is followed by 2–3 weeks of Dry Start under light.
Do not leave a biologically established filter full of water without flow for several weeks. If a longer Dry Start follows the Dark Start, keep the filter safely running in a separate circuit, or after the final fill check NH₃/NH₄ and NO₂ again and do not rush the introduction of animals.
Planting the remaining plants
- Keep the substrate and hardscape damp with a spray bottle.
- Plant as much of the planned area as possible at once. If the composition allows it, I aim for approximately 70–80%.
- A larger mass of healthy plants helps stabilise nutrient uptake more quickly after the lights are switched on.
Final filling and water
Fill the tank again slowly over a sheet. With RO water I mineralise according to the target of the specific aquarium; as a common starting framework I use approximately:
Normal operation and maintenance
Light and CO₂
I switch CO₂ on approximately 2 hours before the lights. I use the drop checker as an approximate guide — a light-green colour confirms the right direction, but it is not an exact measurement of CO₂ concentration.
| Period after planting | Lighting time | Starting intensity |
|---|---|---|
| Weeks 1–2 | 6 hours | 50–60% |
| Weeks 3–4 | 7 hours | around 70% |
| From week 5 | 8 hours | gradually towards the target output |
I do not increase intensity automatically just because the calendar says so. Plant growth, algae condition and CO₂ stability are decisive.
Fertilisation
I usually start micro- and macronutrients approximately 3–5 days after planting, once the plants begin to respond. I use Yokuchi GEN liquid fertilisers according to the current needs of the aquarium.
A safe starting point is roughly half the manufacturer’s recommended dose, then adjust according to plant growth, water parameters and the substrate used.
First animals
One advantage of Dark Start is that the filtration has already been running for several weeks. Even so, I do not introduce animals based only on the number of days. Before each step, NH₃/NH₄ = 0 and NO₂ = 0 must be confirmed.
- 3–5 days after planting: if values are stable, Amano shrimp (Caridina multidentata) and suitable snails can be considered. The aquarium must already provide conditions and food appropriate for the species.
- After 1–2 weeks: add Otocinclus only when there is enough biofilm and natural food in the aquarium — not simply according to the calendar.
- After roughly 3 weeks: the main fish stock, provided nitrogen values remain stable and the aquarium is running without swings.
Dark Start is not a shortcut. It is preparation.
The biggest advantage for me is that the active substrate and filter get several weeks of head start before the plants and animals. After planting I am therefore not dealing at the same time with the substrate’s most intensive phase, fresh filter biology and plant adaptation.
Every aquarium is different. If you are unsure about the substrate, filtration, water parameters or a specific schedule, we can go through your project together.
Online consultation ↗Published 25 Sep 2026 · Nature Aquarium / Jirka Pova