Salvinia

Overview

Salvinia (Salvinia natans) is a small floating fern with pairs of oval, fuzzy green leaves covered in tiny water-repellent hairs that keep it riding high on the surface. Like all good floaters it grows fast, soaks up excess nutrients, shades the tank and helps fight algae, and it makes fine cover for fry. A big advantage over duckweed is that its larger, connected fronds are easy to scoop out, so it never becomes the unremovable nuisance duckweed can. It is a tidy, manageable, attractive floater.

Planting & placement

Salvinia is not planted — it floats on the surface and drifts with the current. As with any floater, filter flow tends to herd it into one corner, so a floating ring or a length of airline keeps it in a neat patch and stops it covering the whole surface. Leave open water for gas exchange and feeding. It needs no substrate and no anchoring, and its short roots and dense fronds give fry and shrimp somewhere to hide — see aquascaping for beginners for placing floaters in a layout.

Light, CO2 & ferts

Salvinia grows best under medium to high light; brighter light produces larger, fuller, greener fronds and faster spread. It needs no CO2, taking carbon from the air. As a fast grower it feeds from the water column and acts as a useful nutrient sponge — a regular water-column fertilizer keeps it healthy, and that appetite for nitrate is what helps shade and starve out algae.

Propagation & problems

Propagation is automatic: the fronds branch and divide, and pieces break off to start new plants, so a small starter portion becomes a floating mat in a few weeks. The main problems are browning or melting from wet leaves and its own speed — a thick mat shades your rooted plants and slows gas exchange, so thin it regularly. Unlike duckweed it lifts out cleanly with a net, making control easy. Kept fed, dry-leaved and thinned, salvinia is one of the most manageable and good-looking floaters you can keep.