Planted Aquarium Substrates


Planted Aquarium Hardscape

by Trent Lloyd

The first step in any planted aquarium or aquascape is the substrate, but this introduction also extends to rocks and driftwood. In a tank that features any combination of those three is called a “hard scape” and is an art form in its own right.   Before anything else be sure you are confident in your design, and where stones and driftwood will be placed if used.

If you are planning on using heavy rocks consider using egg crate also known as light diffuser or light grating down first.   If you’re using gravel the plastic grate will need to be flush to the glass so you will need to get that perfect before adding your substrate.  The plastic grate helps distribute the weight of the rocks and helps avoid breaking the glass of your tank.

The trick to growing great plants is in the roots, and what substrate you use for your scape can have a profound effect on growth. The roots themselves need plenty of oxygen, and this is because the fertilizers are utilized by bacteria growing on the root tendrils, it’s these bacteria that produce the nutrients plants need in a form they can absorb and make use of. Much in the way a filter works by surface area, so surface area plays a role in plant growth by providing more places for this bacteria to do its thing.

Substrate Types

coarse sandWhen considering substrate there are three main groups; sand, stone, and soil. The first, sand has its own variables in color and construct.  While white silica sand is readily available as a substrate, bear in mind the silica in the sand promotes diatoms, ( brown algae ) which in itself isn’t so bad.  It can be problematic if the sand needs to stay in place undisturbed.

Black silica on the other hand is made up of a lager glass chip type structure, which can damage the barbels of bottom dwellers like the loaches, so bear this in mind too.

Another alternative is propagation sand,  available at garden centers or pool shops. It provides a very natural mottled effect, and does not suffer the same issues with Diatoms. It also settles out well and does not stir. It is also great for plant roots with a myriad of airspaces between varying sizes of grain.

A third option is blasting sand,  available at tractor stores and home improvement supply chains. Blasting sand comes in white and black, but can still be sharp so check before you buy.  Beyond that you can seek out rarer sands either from a landscape supply or from wild sources. Lakes are great for this, so are certain beaches. If you want a golden sand some play sands are great, though the gold variety can be hard to find.

Even harder but even more desirable is Kaiteriteri golden sand but so too are river stones and many other raw sources. If you do do this avoid picking up too many shells, as in water that’s already above pH 7 this can make things harder for most species of plants, which prefer acidic conditions, coral sand will also do this . Many cryptocorynes, java fern, saggitaria, vallisineria and mosses all do well in higher pH and even brackish conditions. Also be aware. of potential toxins from run offs, drain outlets, etc.

One thing to be aware of is that finer grains of sand will settle over time, and that will make oxygen less available, even becoming anoxic. This will choke a plant and promote fungus, as well as producing not so nice compounds like hydrogen sulphide and others which can be harmful to fish. One way around this is to mix in gravel of a suitable grain.

With any project consider the color scheme, and what will work best for you, dark colors are great for showing off the colors of fish.  Darker colors also tend to make them feel more comfortable as many natural substrates are darker. Darker substrates can also make a scape seem smaller, much in the same way a painting a small room in dark colors makes it feel smaller

Fluorite is a raw mineral high in the minerals plants need to thrive.  It’s more expensive but pays off with plant growth, and has the added benefit of appearing much like black sand and earthen shades.  Fluorite can be rinsed, but the fines are also good for the plants. So unlike all the other sands and gravels does not need to be rinsed, and is best not rinsed but will more likely cloud when disturbed.

The next gravel is aragonite, which is white, but again this media causes pH to rise, and is used for this property to create the conditions suitable for African lake cichlids, so isn’t the best choice for a soft water planted tank. This also comes in the form of larger round stones and has the same properties.

Occasionally you may be able to find volcanic gravels to choose from, scoria  being one that is high in iron among other things. And the more solid forms provide extra surface area that is great for promoting root growth.

If you do want to use river stones, from an actual river, consider treating with 1 part bleach with 20 parts water after rinsing thoroughly , and by thoroughly, you can’t overdo it.

Soil as a Substrate

Soil is arguably one of the best substrates for promoting vibrant and lush plant growth. Soil has the great ability to store surplus nutrients and provide a slow release to the plants as required. This process will typically last two years or more, but this doesn’t mean fertilizers shouldn’t be added, as it will expire in its own time and the additional supplies serve to “recharge” the substrate. One thing to be careful of is the potting mix or seed mix with slow release terrestrial fertilizers, which while great is typically higher in phosphates and in the absence of an immediate demand form well established plants can bring on troublesome algae blooms.  Terrestrial plant fertilizer often has its nitrogen source in the form of ammonia, which is not a good option for the aquarium.

Many soils are suitable, but they should be considered on their loam content. Loam is soil made up of stone, sand, and organic matter, however the higher the organic compound, the higher the nutrient potential.

There are several companies that produce an aquatic mix which is the preferred choice for most. Most also will cap a layer of soil with a layer of sand or gravel to prevent it from being stirred up in the tank. It can be done neatly if care is taken not to disturb it too much. One issue with capping soil is that eventually plants will need to be removed or added, and this process can effectively disturb the layers and turn into one big mess. So bare this in mind in relation to your level of experience of you which to try it.


Last but not least are the clays. Clay is a fantastic source of chelated minerals, which simply means compounds that are readily available for uptake by the plants.  This is especially so with red clays, which due to the high iron content are ideal for promoting color in red plants.

Laterite is the ideal form, but other red clays are very good as well. Laterite is a unique form of rock that is formed in specific conditions where soluble minerals bond and form a kind of plant “superfood”. Laterite is usually widely available though it is very expensive at around $1 a gram vs the $1 per kg of most sands.

Another option of you don’t want to work with all the potential for mess the clays and soils present you can opt for the best of both in the form of fired clay balls, which still provide the high value chelated minerals of clay and the oxygen content of organics like soil. Clay balls, also called hydroton, go in easy and are much lighter than the raw forms, which can mean a lot when dealing with a scape that features terraces, or reaches high in the back, such as behind rock walls. It could also serve as a base layer and be capped with a substrate that still meets the designer’s aesthetic needs.

When filling the tank use a small plate in the bottom of a plastic shopping bag and fill into that to avoid stirring the substrate, this works with all the media, and should be used during large water changes.  Whatever substrate you choose, bear in mind you will want a fair amount to spare when finished, and this will be used to patch holes and assist with planting extra plants etc.


Collecting RocksWhen choosing rocks for your design, again consider color scheme and weight. The best rocks are highly detailed and have naturally worn faces, much as you would expect in an actual waterway. Ignimbrite is igneous (granite) rock found throughout much of the world, and is often used in sea walls and roadworks. If you do find something you like near a busy road, be sure to treat thoroughly with home brand bleach followed by a treatment with prime and crushed coriander to remove any potential heavy metals.

Better yet source rocks from a landscaper, gneiss slate is the perfect example. Tile slate is an especially interesting option, as it can be broken down, stacked and glued into place to create artificial rock walls.  Most slate is quite soft and can be drilled rather easily.  A carpenters hand saw will also cut most slate with little more effort than hardwood.  Work slowly and deliberately with the saw to make your cuts.

A word of warning, many adventurous hobbyists feel inclined to stack large rocks in the aquarium. This is better avoided if at all possible, as well as the risk of the rocks falling and impacting the glass is high and does happen, more often though fish are crushed when the structure collapses. For this reason if a rock stack is the goal consider using silicon glue and allowing it to set for 48 hours before adding to the aquarium. The same goes for weighting down wood in the tank rather than waiting for it to waterlog first.

Some more interesting rocks include the sandstone form called “dragon stone” which is riddled with Swiss cheese like holes. Rotten rock on the other hand has deep earthen tones, and volcanic rocks come in a wide variety of shades and profiles. Basalt can also make for a unique look.


DriftwoodThere are many forms of driftwood but not all are ideal.  Avoid any wood that is soft or brittle, as it may crumble and deteriorate in a tank. Hardwoods, and especially the hardwood heart of a tree and established root systems are ideal.  Most driftwood from pines and other similar trees do not make good driftwood because of the resin in their wood.

One of the best forms available to us is “spider wood”, which is available at most pet stores that sell fish. Choose carefully, and know what forms you want before you decide. Unless it has a purpose, the most intricate pieces can turn into a headache if they don’t have a definitive role to play. Whilst it appears light colored on the shelf , once waterlogged it will take on a rich dark brown tone.

Boiling driftwood is an effective way to draw out tannins which will otherwise stain the tank water tea colored. Boiling also helps to water log wood, but most will need to be left in a bucket with a heavy stone on top in order to sink the wood before trying to place in the aquarium. With larger pieces this process may take longer than desired. If so, consider using tie tags or stainless steel screws to affix the wood to a flat stone.

Wood collected from freshwater environments is the most ideal, river beds and boulder traps, even the bush itself are great sources. While you may find the perfect piece on a beach, consider whether that piece hasn’t been floating in a back corner of a port amongst potential toxins. Even with treatment like boiling and soaking (recommended regardless) one must accept a potential risk.

Once water logged, driftwood makes a great home for such plants as the ferns; Indian, Javan, Africans, and the anubias, which need their roots exposed to the water, but benefit from having a surface to adhere to.

A few moments forethought into building your hardscape will improve your end results.  Substrate, rock, and driftwood choices are important when planning and building an aquarium.  Make sure you know your tank inhabitants requirements also and take that into consideration.  With the right combination of hardscape components you can make a great looking aquarium.

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