Mosses are not only land plants. A handful of true mosses grow happily underwater, and they are among the most useful plants in the aquarium: undemanding, slow to outgrow, and the natural cover for fry and shrimp.
The usual suspects
- Java moss (Taxiphyllum barbieri): the classic, nearly indestructible, grows in almost any light.
- Christmas moss (Vesicularia montagnei): tidier, with a fir-branch shape, a little more demanding.
- Flame moss (Taxiphyllum "Flame"): grows upward in twisting flame-like columns.
- Weeping moss (Vesicularia ferriei): trails downward, lovely draped over wood.
Attaching it
Aquatic moss does not root into substrate; it clings to hard surfaces by rhizoids, exactly as land moss does. Tie or wrap a thin layer over wood or rock with cotton thread or fine fishing line, or use a dab of cyanoacrylate gel. Spread it thin; a thick wad rots underneath because water cannot reach the inner strands. In a few weeks it grips on its own and the thread can be removed or will simply rot away.
Light, flow and trimming
Most aquarium mosses are content in low to moderate light and do not need added carbon dioxide, though brighter light and CO2 give denser, neater growth. Gentle flow keeps debris from settling in the strands, which otherwise traps muck and starves the moss. Trim with scissors to keep the shape; the clippings will start new patches wherever they settle.
What moss does for the tank
Beyond looking good, moss pulls real weight in a planted tank. Its dense tangle grows the biofilm that shrimp and young fish graze, and it gives fry and shrimplets both food and cover at the moment they are most vulnerable, which is why breeders treat it as close to essential. It also offers a surface for beneficial bacteria, mops up a little excess nutrient, and shelters the small invertebrates that round out a tank's ecology. For dwarf shrimp in particular there is a dedicated piece on how moss benefits Caridina and Neocaridina.
Aquascaping with moss
Aquascapers prize moss because it does what almost nothing else underwater will: clothe hardscape. Tied thin over branching wood it reads as foliage on a miniature tree; bound to a flat stone it makes a mossy boulder; grown on a mesh panel it becomes a wall or a lawn. The look depends on trimming, since an untrimmed clump turns shapeless and shades out its own base, so regular light scissoring keeps it crisp and healthy. Growing the carpet in emersed first, by the dry start method, gives the densest, most even result; both that and bulk-growing are covered in how to propagate aquarium moss.