A planted aquarium is not a fish tank with some plants dropped in it. It is a small ecosystem where light, carbon, nutrients and waste are in balance, and the plants are the primary consumer of the waste. Get that balance roughly right and the tank is stable and largely self-maintaining. Get it wrong and you spend a year fighting algae.
The good news is that the order of decisions is not complicated, and the first one — how big — constrains everything else. This guide works through that order. It assumes no prior experience and no specialist equipment.
Start with the size, because everything follows from it
The instinctive choice is a small tank: it costs less, it fits on a desk, and it looks manageable. It is also the hardest size to keep stable. Water chemistry is a function of volume, and 30 litres has almost no buffering capacity. A small error — an overfeed, a missed water change, a warm week — swings the parameters of a nano tank hard enough to kill livestock. The same error in 120 litres is absorbed.
A 60 cm tank holding around 60 litres is the sensible first aquarium. It is large enough to buffer mistakes, small enough that a weekly water change is one bucket, and it is the size at which a genuine carpeting plant becomes possible. Almost every layout style scales down to it.
Then decide the light and CO₂, because they set the ceiling
Everything a plant does is driven by photosynthesis, and photosynthesis needs light and carbon in proportion. This is the single most important relationship in the hobby and it explains most algae problems.
If you supply strong light and no added CO₂, plants cannot use the light. Algae, which need no added carbon, can. The result is a bright tank with stalled plants and an algae bloom, and the keeper usually responds by increasing the light, which makes it worse. Conversely, moderate light with no CO₂ injection produces slow, easy growth and is very forgiving.
| Approach | Light | CO₂ | Growth | Difficulty |
|---|---|---|---|---|
| Low-tech | 20–40 µmol/m²/s | None added | Slow | Forgiving |
| Medium | 40–80 µmol/m²/s | Optional, liquid carbon | Moderate | Moderate |
| High-tech | 80–150+ µmol/m²/s | Injected, ~30 ppm | Fast | Demanding |
A first tank should be low-tech or low-end medium. You can always add CO₂ later; you cannot un-buy an overpowered light that you then have to dim permanently.
Choose the substrate before you choose the plants
Substrate is the one component that is effectively permanent. Changing it means emptying the tank, and in a planted tank the roots are the whole point. There are two routes.
- Aqua soil — sintered clay granules that buffer pH down and hold nutrients for roots. It releases ammonia for the first two to six weeks, which is why a new aqua soil tank must be cycled empty. It exhausts after 12–24 months.
- Inert sand or fine gravel — chemically neutral, so the water is whatever you make it. Nothing is available to roots, so heavy feeders need root tabs pushed in beside them every two to three months.
Aqua soil is the better substrate for a planted tank and it is what most aquascapes use. Sand is the better substrate for bottom-dwelling fish with delicate barbels, and for anyone who wants predictable water parameters.
Cycle the tank, and understand what you are waiting for
A filter does not clean water. It hosts bacteria that convert ammonia — toxic — into nitrite — also toxic — and then into nitrate, which is much less so. Those bacteria take weeks to establish, and until they have, ammonia from any source accumulates.
Set up and plant
Substrate, hardscape, plants and filter running. Plant densely from day one; a sparse start leaves light and nutrients for algae.
Add an ammonia source
With aqua soil, it is already there. Otherwise dose ammonia to about 2 ppm or feed a pinch of fish food daily.
Test and wait
Ammonia falls, nitrite rises, nitrite falls, nitrate appears. This takes two to six weeks and cannot be rushed.
Confirm, then stock
When ammonia and nitrite both read zero within 24 hours of a dose, the cycle is complete. Then add livestock slowly.
A planted tank cycles faster than a bare one, because plants take up ammonia directly and because a mature plant brings bacteria with it. It still takes weeks, not days.
Stock it slowly, and in the right order
Bioload is a rate, not a count. Every fish adds a continuous ammonia output, and the bacterial colony grows to match it — but only over days. Adding twenty fish at once produces an ammonia spike the filter cannot absorb. Adding five, waiting two weeks, then adding five more lets the colony keep pace.
Order matters too. Territorial species should go in last, so that earlier, more timid additions have had time to establish their own space. Shrimp and snails can go in early once the tank is mature enough to have biofilm for them to graze.
What beginners spend money on that changes nothing
- Expensive filter media with branded biological cartridges. Sintered glass or ceramic rings of any brand perform the same job; what matters is surface area and not washing them under a tap.
- pH adjusters and buffers. Chasing a target pH with chemicals causes swings that are far worse than a stable value slightly off target. pH is set by substrate, water source and CO₂.
- Medications bought in advance. Most are unnecessary, several are harmful to shrimp and snails, and all of them expire.
- A larger light than the tank needs. The commonest upgrade regret in the hobby, and it is almost always the cause of the algae problem that follows.
The routine, once it is running
A planted tank in balance needs very little. A 25–30% water change weekly, a trim when the plants reach the surface, a filter rinse in tank water every four to six weeks, and a test before the water change. That is the entire routine, and skipping the water change is the single most common reason a stable tank stops being stable.
The first two months are the hard part. After that, a planted tank is largely a matter of not interfering with it.