How to grow lush planted tanks without CO2 injection?

The term 'low tech' has nothing to do with actual technology; it simply refers to planted aquariums that operate without injected carbon dioxide (CO2) - this is due to historical convention, when CO2 injection equipment was considered high tech in the past.

However, many plants can grow well without injected CO2, and a thriving planted aquarium without CO2 injection is well within the capabilities of most aquarists. This approach requires far less equipment and technical knowledge than CO2-injected tanks, and many fish-only setups can be easily converted to thriving plants with a few clever tweaks. The plants provide a great environment for the fish by filtering the water and providing a natural environment.

Below: a lushly planted low-tech tank by John Chang with a mix of easier and slightly harder plant species. A good understanding of what makes a low-tech tank work well allows us to have lush, healthy tanks without the need for CO2 injection.

Six steps to an amazing 'low-tech' tank

Step 1: Choose these plants

Choose a plant selection that works with low CO2 conditions. This include plants such as Java fern, Anubias species, Water wisteria (Hygrophila difformis), Dwarf saggitaria (Sagittaria subulata), Vallisneria species, Ludwigia Repens, Java moss, Marsilea species, Rotala rotundifolia, Pearlweed ( Hemianthus micranthemoides), Sword plants, Red/green lotuses (Nypmhaea Zenkeri), Water sprite (Ceratopteris thalictroides).

A low tech planted aquarium by George Farmer from the UK. Check out his instagram and youtube channel. This tank shows some great choices for a low tech tank. Cryptocorynes are used on the substrate and narrow-leaved Java fern on the hardscape. The red plant on the top left is limnophila aromatica. This tank also shows how a substantial hardscape (compare the size of the wood to George standing to the side) forms the backbone of the aquascape.

For a guide to the best low tech plants, click here.

Step 2: Focus on Hardscape

Choose 'easy' plants, but implement complexity through hardscape work. This approach delivers much better results than being overly ambitious with demanding plants.

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This hardscape-only tank on the by ADG group (visit them to get your hardscape materials) shows that hardscape alone can create stunning aquascapes.

Step 3: Use Soil

Use a soil-based planted aquarium substrate. Low-tech soil-based planted aquariums consistently outperform those using inert (sand/gravel) substrates. They provide a long-term store of nutrients for plants. The organic decomposition of the soil releases carbon to aid growth.

Many plants root better in soil and it encourages bacterial colonisation which has a stabilising effect on the aquarium environment. It also offers much better success rates for growing plants that otherwise require CO2 injection to grow well - these include plants such as Monte Carlo, Staurogyne repens & Alternanthera reineckii.

Commercial pellet aquasoils are much less messy to handle than using raw soil, and give more predictable results due to the consistency of the product.

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A one gallon low tech vase using a mix of raw soil with an aquasoil cap. The pelleted commercial aquasoil keeps the fine particles of the raw soil down and is easy to plant in.

To learn more about substrate, click here.

Step 4: Plant densely at the start

Planting densely at the start will prevent algae from gaining a foothold. Plants have a stabilising effect on the tank's ecosystem and help to absorb waste products such as ammonia and heavy metals.

The tank should be at least 50% planted at the start. A sparsely planted tank is an invitation for algae to spawn and take over the space. Most tanks reach stability when the plant mass dominates 70%+ of the available space. A fully planted tank is the best defence against algae.

This is a mini 3 gallon low tech tank using raw soil as planted aquarium substrate base. Tank is virtually algae free as healthy plants out-compete algae.

Step 5: go for shallower tanks

Shallow tanks are much easier to manage. They have inherently better gas exchange and you have easier lighting options - it is much easier to light a shallow tank than a deep one. This has a greater impact than most people realise. Low tech tanks benefit enormously in this respect.

A wide shallow tank such as this one by Tom barr makes it easy for aquatic plants to grow above the water surface.

To learn more about tanks for aquascaping, click here.

Step 6: Doze in small but regular amounts

Low tech tanks also do far better with regular fertilisation. Small weekly doses of fertiliser is sufficient."No fert, no dirt" tanks are essentially a bet that your water supply contains all the essential elements for plant growth. 

Livestock waste is rarely adequate for optimal plant health. No fish I know of poops out chelated iron for example. Unless you are sure your tap is rich in all the required elements, having regular doses of fertiliser impacts plant health greatly.

Dosing large amounts of nutrients (EI style heavy dosing) is an invitation to trouble. A tank with low demand plants, such as those shown below, only needs to be fertilised once or twice a week at much lower levels. Consider a comprehensive fertiliser such as APT 3 (if you have very few or no fish) or APT 1(if you have moderate to large numbers of fish/other animals).

​This layout by Hiep Hong demonstrates good use of hardscape. This would make a terrific display tank for fish with relatively low maintenance required.