Planted Aquarium Substrate

The substrate serves two purposes in a planted aquarium. It provides a suitable medium to anchor the aquatic plants. Secondly; it provides nutrients required for aquatic plant growth. While there are many suitable types of substrate, sea sand (such as Philippine sand and South China Marine sand), plain fine river sand and aquarium gravel are fairly popular. Some alternate substrates used by aquarists are fired red clay, Fuji sand, volcanic sand, and ceramics.

Substrate used for the planted aquarium must meet a few criteria:

• First and foremost, it must not contain elements that adversely affect the water conditions. Most prominent here are coral and seashells, which will raise the pH value and water hardness because of their high calcium content. Other materials that lower these two values can cause root to rot, which in turn leads to algae growth. The pH value of the sand itself should be neutral to slightly acidic (6.5 to 7), the ideal for most plant roots. 
• The granule size should be somewhere between 3 and 10mm. Larger granules will stifle root development, and sand made up of smaller grains will crush the roots. Base sand that is not permeable enough, like unfired clay, blocks the passage of important particles and prevents the flow of oxygen that the roots need. Sand that isn't smooth in texture, especially those with jugular edges will damage roots during planting. If you are unsure, have a lab examine it under a microscope.

Any base substrate that meets these conditions is safe to use in an aquarium, but glass beads, colored ceramics, and other unnatural materials are not recommended for aesthetic reasons. 

Next, let's consider the types of substrate for cultivating different types of aquatic plants. There are three broad groups of aquatic plants classified by root types. First are the plants that don't require susbtrate to grow, but instead attach their roots to rocks or driftwood, plants such as Anubias, Microsorium, and Bolbitis. Next are the plants with large root stocks, like Aponogeton and Nymphaea, and the long-stemmed plants, like Hygrophila and Rotala, that have shallow roots. Lastly, are deep-root plants like Cryptocoryne and Echinodorus. 

These plants all have corresponding substrate needs which must be met. If the substrate is not deep enough for the last type, for example, the roots will become entangled and the plants, which obtain most of their nutrients and oxygen through their roots, will be asphyxiated. Echinodorus tenellus and E. grisebachii, both of which have long rhizome runners, need at least a 6cm deep substrate. 

When the aquarium contains all three root types, as it often does, it is necessary to create a substrate that will accommodate the deep-rooted plants. Substrates that contain several different types of sand will have a longer lifetime, and arranging them in layers improves permeability. For example, for the bottom layer mix 5-10mm granule sand with 5-10mm size Fuji sand. Add in some sand based substrate fertilizer, which can be bought in stores. Smooth out the layer at around 3cm. For the middle layer, repeat the procedure minus the fertilizer and with slightly finer sand and Fuji sand (5-7mm) Finally, for the top layer add 2cm of fine 5mm granule sand alone, this will provide the grip for your plants during initial planting. Fuji sand, and other sand of volcanic origin, are too rough for the surface substrate since it will damage your roots.

Fuji sand is mixed in to prevent lumping and hardening and to improve permeability. The roots of Echinodorus and Cryptocoryne are comparatively thick, and the spaces between regular sand are just too tight for them. If Fuji sand is unavailable, it is best to mix sand of different granule sizes. It is safe to use pre-mixed sand such as the Malayan or Amazonia soil sold by ADA, Japan.

Fertilizer should be added only to the bottom layer of the substrate to prevent it from seeping back into the aquarium water, this will also help to prevent algae growth of various types. When filling the tank, the water should be poured gently into a plate or bowl placed on the sand to avoid churning up the fertilizer.