Propagating Chaetomorpha (Chaeto) Macroalgae

How to propagate Chaetomorpha linum, the tumbling marine green macroalgae kept in refugiums, by simply dividing the clump and harvesting regularly to keep nutrient export active.

Overview

Chaetomorpha is a marine green macroalgae made up of macroscopic filaments that are one cell thick and unbranched; this lack of branching distinguishes it from related algae. It is popular with aquarium hobbyists, kept in saltwater refugiums where it exports organic nutrients and offers a refuge for beneficial microfauna like copepods.

It is not a substrate stem plant but a free-floating tangle that grows as a loose ball or mat. It is considered the easiest macroalgae to grow and harvest in a refugium, growing fast and rarely crashing.

Propagation Method

Propagation could not be simpler: the alga reproduces by filament fragmentation, so you just pull off or divide a portion of an established clump and let both halves continue tumbling and growing under light and flow.

Step-by-Step

1. Lift a handful from an established, healthy clump in the refugium or sump.
2. Pull it apart or divide it into the portions you need — no cutting tools or attachment are required.
3. Place each portion back into the refugium under the light, leaving room to tumble.
4. Harvest excess regularly to keep active growth, since growing algae is what drives nutrient export.
5. Use harvested portions to seed another refugium or share with other reefers.

Conditions for Healthy Growth

Light the refugium well, around 6700K; some aquarists run the light 24/7 so the macroalgae outcompetes nuisance algae in the display. Keep flow low so detritus settles, while ample nutrients (nitrate and phosphate) from the system feed fast growth. For real nutrient reduction, run a large amount — far more than you might expect.

Maintenance

The core maintenance is regular harvesting: removing a portion every couple of weeks keeps the colony in active growth, and each harvest is itself a propagation event that physically exports the nutrients locked in the tissue.

Common Challenges

Too little light or flow leaves the inner mat shaded and clogged with detritus; too small a clump exports little. Never dump specimens into waterways — improper disposal has established invasive non-native populations, so boil, freeze or dry surplus before discarding.