High-intensity lights and high-pressure carbon dioxide (CO2) injection. Traditionally, these are the key ingredients needed to make stunning aquascapes. Yet that’s not available to me, and not available to many, as all that gear costs a pretty penny and requires dedication to master and maintain. In contrast, ‘carbon (dioxide) free’ low-tech aquascaping is the preferred choice for those looking for lower maintenance and lower costs. And low-tech does come with lazy benefits — slower growth means less pruning, less urgency of nutrient dosing, smaller waterchanges and even less circulation pumps to clean.

What’s not to like?

Unfortunately, and especially for the inexperienced hobbyist, low-tech aquascaping can still be disastrous. For example, it is generally recommended to initially stock a low-tech aquarium heavily with plants, as the slow growth rates of such plants leaves them at mercy of algae if too few are added. Yet the range of suitable plants for a low-tech tank is smaller and the risk of plants struggling and dying all
that much greater.

In fact, you’d not need to look far to find an unfortunate newcomer watching in despair as the Staurogyne repens and Hemianthus callitrichoides ‘cuba’ in their tank wither or dissolve under ill-considered lighting, to be replaced with black brush or diatom algae and an army of snails. So, what am I concluding here? Is being cheap and lazy possibly more complex than high-tech CO2 injected systems? If so, what can we then recommend for the starter aquascaper?

Mucky plants

In order to understand the complexities of any planted set-up, we should at the basics. Plants use light to grow (as they photosynthesise) and for this process they also need nutrients and carbon dioxide. In fact, optimal plant growth relies on a trinity of light, food and CO2, and a plant’s rate of growth is limited by whichever of these is lacking. You could add heaps of lighting and CO2 to a tank, but without food the plants won’t grow. Likewise, a tank with abundant plant food and CO2 but really dull lighting will struggle— for all the nutrients and gas, the plants lack the light energy to do anything with it. Balance is key.

Based on that, it’s obvious that the greater the amount of light aquarium plants receive, the more nutrients and CO2 they need. A simple way to meet this demand is to add fertilisers. These can be added in liquid form (directly in the water column), and/or in solid form (in the form of soil or planting tablets), as well as in the gaseous form (CO2 introduced from cylinders). And as anyone who has studied basic biology will know, plants use the carbon (C) present in CO2 to grow and return the oxygen (O2) back. So far nothing new...

A lesser-known aspect is that, besides ‘breathing’ CO2 and O2, plants also ‘pee’. Well, to put it more scientifically, they excrete organic waste. However, unlike the ammonia produced as fish waste, this plant waste is not as easily broken down using a filter.

In addition to this, organic plant waste has a negative influence on the growth rate of plants. Ironically, plant waste does not seem to have a similarly inhibitory effect on algae growth, which implies that the more plant waste that builds up, the more favourable the conditions become for algae growth. Accordingly, one of the best methods to enhance plant growth and lower the chances of algae formation is to do large water changes (combined with dosing of fertilisers). This also helps explain why in systems with ample light, CO2 and other fertilisers, ‘pearling’ (the forming of small but numerous oxygen bubbles on plants) occurs most distinctly directly after (large) water changes. For after the water change, the lack of plant waste combined with a surplus of nutrients and light make the growth rate (and by extension the rate of oxygen formation) skyrocket.

However, this also leads to a rapid boost in the amount of organic waste formed by the plants, which in turn begins to reduce their growth rate. Once the growth rate is lowered again, the pearling ceases. In short, plants don't seem to like standing in their own pee. So now we have the general picture: in order to maximize plant growth, we need strong lighting, plenty of nutrient-rich aquascaper soil, liquid fertiliser, dosing of CO2, and — and this is the important bit — loads of water changes. In a clinical sense, these all represent the core ingredients of high-tech aquascaping.

Going wrong

So, what does aquascaping ‘failure’ look like? Generally speaking, two (related) types of failure occur. The first is that your freshly-purchased plants do not grow or even start to slowly die and melt away, while the second is the abundant and persistent formation of different types of algae. Although subject to ongoing debate, both the melting of plants and algae formation can be related to an imbalance in the items we’ve just looked at: fertilisers, gas content and water changes. As with most good things, a sense of balance is implied.

Back to basics

Alrighty then, with the basics laid out, let’s face the last key question. What actually is ‘low-tech’ aquascaping? Generally speaking, a variety of approaches may claim to be low-tech. Still, most options feature two common aspects. The first is the absence of any additional CO2, while the second is a reduced rate of water changes (as compared to a high-tech aquascape). On this second point, it’s common for a low-tech tank to receive a waterchange no more frequently than two weeks apart (and often much less frequently than that).

Importantly, any tank without added CO2 has a lower potential growth rate for plants compared to one that does. But on the other hand, the requirement for the considerable water circulation necessary for CO2-powered tanks — up to 10 times the tank’s volume every hour — is less critical. With CO2 injection, flow is essential to ensure that the gas is distributed evenly throughout, which for a ‘CO2-free’ set-up isn’t an issue.

With that out of the way, let us now finally discuss two fundamentally different scenarios of low-tech aquascaping. One where we start with a lusciously planted aquarium and only liquid fertilisers in the water column, and the other in the same tank with fertiliser present only in the soil.

Where to fertilise

In the case of fertilising only the water column, getting the light intensity right is vital, as using too much of it can easily turn the tank into an algae-infested mess. This is because of the imbalance between high levels of nutrients in the water column and low amounts of CO2, and is compounded in a tank where water changes aren’t carried out regularly, and plant growth is further inhibited by their own ‘pee’. In order to calibrate the planting ecosystem to a low level of CO2, we should reduce the growth rate, which means reducing light intensity. Doing so will concomitantly enable us to get away with a lower amount of water changes.

Most aquarium kits these days provide high-intensity light systems, making, especially for low-tech aquascaping, some degree of control over the lighting intensity a necessity. LED-based systems, for example, commonly feature high intensities of about 0.3 W/L. For a water-column fertilised low-tech system, my own experience has shown that this is best reduced to closer to 0.1W/L. If the amount of nutrients is then also reduced by a similar factor as the light intensity, a more balanced (and more likely algae-free) system is obtained.

In tanks where plants are solely fertilised through the roots via soil fertilisation, the water column should be largely free of nutrients. This represents a complete game changer as, without nutrients, algae should not stand a chance. Under high lighting, the challenge in this scenario is to ensure that no excessive amounts of nutrients get into the water column, and so to start, any melting of plants and organic detritus should be removed asap from the tank. Setting up can be tricky as large amounts of nutrients may be released from the fresh aquascaping soil — every time the soil is disturbed, some nutrients escape from it into the water. With this is mind, any uprooting of plants during maintenance should be followed by large water changes. Light fish stocking is also recommended in order to keep the (fish) waste-derived nutrients in the water column low.

Further considerations

Both water-based nutrient and soil-based nutrient low-tech aquascaping approaches have profound consequences on several other aspects. In terms of plant choice, the two scenarios favour different types of plants. For example, using the water-fertilised set-up, a lower light intensity implies that many medium-to-high demanding light species may not thrive (such as Staurogyne repens and any of the carpeting plants).

In addition, the growth rate of heavy root feeders (such as Vallisneria and Amazon swords) may be reduced due to the limited ferts available in the soil. In contrast, when fertilising only the soil, plants taking their nutrients from the water column (such as ephiphyte plants like Java ferns, Anubias and Bucephalandra, as well as floating plants and certain fast-growing stem plants) may suffer. In each of these cases, long term ‘tank syndromes’ may occur. In the case of the water-column fertilised systems, waste of fish and plants can start to penetrate the soil over time, giving rise to the eventual release of nutrients for the roots. This suggests that a new tank may slowly become more suitable for root feeding plants over time. In contrast, the soil of the rich soil-fertilised system may eventually become depleted of nutrients, giving rise to a lower growth rate of root feeders in time.

Make it happen!

With all this wisdom, let’s have a go at making the ultimate beginner recommendation for a successful one-hourly maintenance per week low-tech tank. Let us consider an aquarium of about 50-100 l. For this size initial heavy stocking with plants will not be overly expensive and at the same time water changes will not take too long. Also, the height of the tank should enable you to still grow most sizes of plants. Make sure the LED-based light unit can be controlled in intensity and set it at about 0.1W/L, and keep it this way for a cycle of eight hours. But don't put the lights on just yet!

With that arranged, add a proven plant soil (at least 10cm deep), add your hardscape, fill with water, and run your tank in the complete darkness for about three weeks. This helps to cycle your filter and soak up any excessive nutrients released by the soil or hardscape in the water. After this period, empty your tank to just above the soil, and purchase your plants. Focus only on ‘easy’ plants and include at least 50% of fast growers.

Suitable plants include: Dwarf sagittaria, Sagittaria subulata (fast growing); Vallisneria (fast growing); Anubias; Java fern, Microsorum pteropus; Amazonian swords, Echinodorus sp. (fast growing); and perhaps some mosses.

Now, for the best part, release your inner ‘artiste’ and ‘scape these plants and hardscape into an unprecedented underwater Babylon garden. Finally, add some surface plants, making sure that never more than 30% of the surface is covered (in order to maintain sufficient light for the submerged plants).

Finally, add fertiliser to the water column at a dose of about a half as compared to a high-tech system (for example based on values for the EI method) and replace 50% of the water once a week for 1 month, followed by light fish stocking. Then, and only then, we arrive at the final destination — a beautiful CO2-free aquascape of which we change 50% of the water only once every two weeks. Good luck!