The three kinds compared
| Kind | Examples | What it gives plants | What it does to the water |
|---|---|---|---|
| Sand or plain gravel | Aquarium sand, pool filter sand, natural gravel | Nothing of its own; root tabs feed the roots | Nothing, unless it contains limestone or shell, which raise hardness and pH |
| Mineral gravel | Seachem Flourite, CaribSea Eco-Planted Black and Red | Iron and other minerals in the grains; Seachem says Flourite never needs replacing | Flourite does not change pH, by Seachem’s description |
| Volcanic soil (aqua soil) | Fluval Stratum and Bio-Stratum, CaribSea Pyroflora | Nutrients in light, porous granules that roots spread through | Stratum softens the water and lowers KH, holding the pH neutral to slightly acidic, by Fluval’s description; CaribSea sells Pyroflora for soft, mildly acidic water |
CaribSea renamed Eco-Complete Planted as Eco-Planted; it is the same product. Its black version is based on volcanic basalt with iron, calcium, magnesium, potassium, sulfur and over 25 other elements; the red one is based on laterite, an iron-rich tropical soil.
Which one for your tank
- Java fern, anubias, crypts and swords in a low-tech tank: sand or gravel with root tabs is enough. The ferns and anubias grow on wood and never touch the substrate. Low-tech planted tank
- Carpets and fine-rooted plants: small grains. Fluval makes Bio-Stratum at 1 to 3 mm for fine, delicate roots and Stratum at 3 to 5 mm for plants with bigger root systems.
- Shrimp: a soil keeps the water soft for crystal red and other Caridina shrimp, and Fluval says Stratum gives newborn shrimp a refuge from predators. Cherry shrimp do well on any substrate.
- Corydoras, kuhli loaches and other bottom fish: sand or small, rounded grains, since they sift through it with their barbels. CaribSea suggests its Eco-Planted Red for planted tanks with soft-bellied bottom fish.
- Livebearers, goldfish and African cichlids: leave out the water-softening soils, since these fish want hard water. Use sand or gravel with root tabs.
How deep, and how much to buy
Lay about 2 to 3 inches where swords, crypts and vallisneria will root, and 1 to 2 inches is enough under a carpet. Many keepers slope it deeper toward the back, which gives the tall plants room for roots and makes the tank look deeper.
Bags are sold by weight, and substrates weigh very different amounts for the same depth. CaribSea gives Eco-Planted’s density as 54 pounds per cubic foot, so one 20 lb bag lays a little under 2 inches over a 20 long’s floor (about 29½ × 11½ inches inside the glass). The same 2 inches of one of CaribSea’s sands at 95 pounds per cubic foot weighs about 37 lb, while soils are lighter (Fluval calls Stratum lightweight, easier on the bottom glass). For your own tank, the substrate calculator works out the volume for your depth and the bags of any CaribSea substrate. Add it to the filled weight
Putting it in
- Rinse sand and gravel until the water runs nearly clear. Seachem says Flourite is washed but can get dusty in transit, so rinse it too.
- Soils are not rinsed or stirred like gravel; follow the directions on the bag.
- Plant before the tank is full, with a few inches of water in it, or plant into damp substrate for a dry start.
- Fill slowly onto a plate or into a bowl set on the substrate so the water does not dig holes, as Seachem suggests. Some cloudiness at first is normal and the filter clears it.
Feeding the plants later on
A soil feeds the plants most in its first months. As it gives up its nutrients, push root tabs in near the swords, crypts and lilies, as you would in plain gravel. A liquid fertilizer feeds the plants that take their food from the water, whatever the substrate. Fertilizer and root tab calculator