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Starting a planted tank- difficult first steps?

August 08, 2023 5 min read

Starting a planted tank- difficult first steps?


A new aquarium is always lovely but can quickly become frustrating. Algae is often the main culprit, new tanks can face an explosion of algae in the second or third week, usually in the form of diatoms like below. This almost always happens if the tank is run with high light and has not been cycled before planting.

In a new setup even the substrate need time to become biologically mature. Many microscopic changes occur when a substrate is submerged for the first time. Bacteria in the substrate that is used to air has to adapt to submerged conditions. Microbes that are used to being in air are outcompeted by microbes that strive in submerged conditions. Plants that are newly introduced into the tank also need to acclimatize to the new environment. In their adaptation process, they secrete waste proteins and carbohydrates directly through the leaf surfaces as they re-calibrate their enzymes and proteins to match the new environment. All these actions produce volatile organics and ammonia. This trigger various types of algae to spawn on the leaves of plants, smothering growth.

A new aquarium might look clean and peaceful, but on the microbial level, the tank is going through rapid changes. There are many steps that we can take to reduce the incidence of algae and allow plants to settle in more smoothly in a fresh setup.

Step #1: Cycle the tank

In modern fish keeping, the ammonia cycle is well understood. While it is the norm for the fish-keepers to cycle their tanks before adding livestock, the practice is often skipped by folks setting up their planted tanks. This is principally due to the plant love ammonia myth:

Myth: Plants love ammonia!

The myth is that plants LOVE ammonia as they can utilize the nitrogen from ammonia for growth. This statement is a half-truth; plants do utilize ammonicial nitrogen very effectively growth. However, ammonia is also toxic at the same time, so while plants can utilize a small amount of ammonia during their growth window, they also suffer from toxicity when the water is saturated to high levels with it. Ammonia is both useful as well as toxic - plants can assimilate ammonia at the point of growth, but because of its toxicity, plants actually convert the ammonia to nitrate form in order to store it. The amount of ammonia that plants can uptake at any one time is small - the ideal scenario is where plants get a small, continual supply of it (usually through root contact in the substrate). 

Freshly submerged aquasoils can raise ammonia levels in the tank by a few parts per million (up to 3-4ppm in some cases), which is far beyond the useful threshold for aquatic plants. Freshly introduced plants that have not yet fully adapted to the new environment are not in high growth speed - being saturated in ammonia at this point brings no benefits at all.

In fact, high levels burn delicate plants such as smaller plantlets purchased in tissue culture format. This is probably the number 1 reason why folks face melting with tissue culture and other delicate plants.

It is tremendously helpful to cycle a tank before planting. The approach is to let the filter run, with hardscape and substrate in, without lights. If you are using an aquasoil substrate that is of decent richness, it should release ammonia for the first few weeks. We let our tanks cycle for at least a week (2 is better), and add APT Start (which contains starter bacteria culture) to accelerate the cycling. This is sometimes called a dark start, as the tank's lights are turned off during this period. Lights are turned off so as not to trigger algae. The exact steps are detailed below:

- Set up tank with substrate, hardscape.

- Add ammonia (skip if aquasoil releases ammonia), target 1 to 2ppm of ammonia. Add starter bacteria if you can.

- Turn on filter, but not the lights or CO2 system.

- Run the system for at least 1 week.

- Do a large water change (90%) to remove debris and dissolved organic waste.

- Add 1ppm of ammonia. (If you are using an aquasoil substrate that emits ammonia, skip this step)

- Test for ammonia 6 hours later; if you have undetectable ammonia you can move on to planting the tank. For folks that want a more detailed diagnosis of the state of cycling for the tank, you can take Nitrite and Nitrate readings - nitrite should also measure zero while nitrates should give a positive value, showing that ammonia has been converted to nitrates.

- If ammonia readings are still high, continue to let the tank run and cycle.

Tank Cycling

Step #2: Plant at least 70% of the substrate

Many tanks start off sparsely planted, which is a big invitation for algae to take hold.

When adding plants, it makes a significant impact when you have enough plants to immediately cover at least 70% of the tank substrate. A well planted tank is the best defense against algae. Plants have a very significant impact on the micro-climate of planted tanks. When plant mass is dominant and healthy, the tank becomes very algae resistant, even in the presence of higher light and nutrient levels. As plant growth improves and plant density increases, it is almost always paired with a decline in algae.

However, the opposite is also true, unhealthy plants can be big algae magnets. Thus the next step is to ensure that the plants grow in smoothly.

Step #3: Hold Steady, do not change parameters just to compensate for small algae spikes

This phase can often be skipped if the above steps to cycle the tank before hand and plant densely were taken. However, some tanks will still get it in a mild way as plants take time to adapt to the new environment. In CO2 tanks, this is generally a temporary 1-2 week phase if we keep other parameters stable! It is unhelpful to have irregularity in lighting, CO2 and multiple changes in water parameters at this stage.

In tanks without CO2, this phase can take much longer - often 4- 6 weeks easily. This is because plant growth and adaption is much slower without CO2 injection. This can become a major test of patience for many people.

The important thing- refrain from adding a cocktail of strong algicides or changing your fertiliser dosage or adding other additives at this phase. All these tend to prolong rather than hasten the path to stability.

New Tank Diatoms

Below we see the same tank after the diatoms disappeared. We did not change our fertilizer dosing or adjust any water parameters in a significant way.

Tank Cycling 2Hr Way

Step #4: Replant fresh growth, discard old growth

All plants go through an adaptation phase to fit your tank environment. As a rule, plants channel their energy towards new leaves, rather than try to preserve old ones. So it is normal for old leaves to be shed.

For stem plants, always replant the healthy tops after they grow tall, as the new tops are adapted to the tank. Discard old stems and roots. Don’t worry- new roots will grow easily. Aquatic plants are not perennial and losing their roots isn’t an issue at all.

2Hr Way Cutting and Replanting

Instead of simply trimming the first cycle after initial planting, take the effort to cut and replant.

For most stem plants, you can trim in the second cycle (after having replanted the healthy tops the first time) and maybe the 3rd cycle. But by the 5th cycle (the 5th time they grow to hit the water surface) it is often the time to trim and replant again.

Stem plants require a lot more work in that sense.

Summary of key points

  • Dark cycle the tank
  • Plant at least 70% of the substrate
  • Large, frequent water changes
  • Remove detritus and old growth when water changing
  • Use less light for the initial weeks
  • Keep parameters stable
  • Replant new growth and get rid of old growth

Keep to the steps above and you'll have a sparkling tank with weeks.