Substrates

In a planted tank the substrate is more than a bottom cover: rooted plants draw much of their food from it, and useful bacteria live in it. Plain gravel gives plants almost nothing, so rooted species such as cryptocorynes need a nutrient-rich or porous base.

A plant soil, or active substrate, contains nutrients and softens the water, so it suits demanding plants and shrimp. A nutrient layer under gravel feeds roots while the bottom looks ordinary. Lava soil and porous clay substrate give bacteria and roots plenty of surface. Substrate fertiliser with starter bacteria helps a new tank start.

New plant soil releases plenty of nutrients at first, which can trigger an algae bloom; frequent water changes in the first month and dense planting keep it in check. Do not mix soil with gravel or dig through it often. Once nutrients run out, root tabs help.