Cladophora Algae: The Tough Scrubbing Pad Algae and How to Eradicate It

What exactly is Cladophora?

Cladophora is a genus of branching green macroalgae found in both freshwater and marine environments. In the aquarium hobby, the freshwater species causing problems is most commonly Cladophora aegagropila or closely related strains. Unlike soft filamentous algae such as hair algae or blanketweed, Cladophora has a rigid, almost cartilaginous structure. Pull a clump out and it holds its shape. Rub it between your fingers and it feels like a stiff scrubbing pad - that texture is the fastest way to distinguish it from the softer, slippier filamentous algae that typically indicate a nutrient or light imbalance.

It grows in dense, branching colonies that attach firmly to rough surfaces: driftwood, lava rock, sponge filter media, the rough side of slate, even the suction cups on your heater. Under moderate aquarium lighting it can appear dark green to olive. Under stronger light, colonies near the surface may bleach to a pale green or yellow-green. Growth is slow compared to hair algae, which is precisely why many aquarists don't notice it until it's thoroughly established.

How Cladophora gets into your tank

This is where most guides miss the point entirely. Unlike cyanobacteria or green water, Cladophora isn't triggered by imbalanced conditions inside your tank - it's introduced from outside it. The three main vectors are:

Moss balls

This is the big one. "Moss balls" sold in the hobby - including the popular Marimo ball - are technically colonies of Aegagropila linnaei, not true mosses. Genuine Marimo from Japanese and Icelandic populations are slow-growing and densely packed. The mass-produced versions sold in most chain pet stores are often farmed or partially synthetic, and some batches have been found to contain living Cladophora strands mixed in. In 2021, a large-scale recall of moss balls across North American retailers was issued because of an invasive Dreissenid mussel contamination - but the associated algae identification issue highlighted just how inconsistent the "moss ball" supply chain is.

If you're buying moss balls, inspect them closely. Genuine Aegagropila has a uniform, velvety surface. A moss ball with coarser, protruding filamentous strands shooting outward should be quarantined and examined before going into your display tank.

Driftwood and hardscape

Wild-collected or aquarium-traded driftwood that was previously in an infected tank can carry Cladophora fragments. The algae can survive short periods of drying - so simply air-drying a piece of wood for a day or two isn't a reliable sterilisation method. Any second-hand hardscape needs a proper dip treatment before use.

Live plants and botanicals

Tissue-cultured plants are clean by definition, but stem plants, rhizome plants, and wild-collected botanicals (seed pods, leaves) bought from hobbyists or local fish stores can carry fragments. The filaments are small enough to hide in plant leaf axils or curl around stem nodes without being immediately visible.

Identifying it correctly

Getting the ID right matters because the eradication methods differ between algae types, and wasting weeks treating the wrong thing is frustrating. Here's how Cladophora compares to the algae it's most often confused with:

Hair algae (Pithophora / Spirogyra species): Soft, limp, collapses when removed from water. Feels slippery or silky. Usually a response to excess light or nutrients. Cladophora is stiff and holds its shape out of water.

Java moss (Taxiphyllum barbieri): Also forms dense green mats on wood and rock, but has clearly visible leaf-like structures under close inspection. Cladophora is purely filamentous with no leaves.

Staghorn algae: Grey-green, stiff, single or sparsely branching strands. Staghorn tends to attach to plant leaves and filter outlets. Cladophora forms denser mats and favours porous hardscape over plant leaves.

How to get rid of Cladophora

There's no single magic treatment. Effective eradication combines mechanical removal, targeted chemical dips, and media decisions. Do all three - skipping any one of them is why most people find themselves back to square one after a month.

Step 1: Mechanical removal first

Before any chemical treatment, remove as much algae physically as possible. Use a stiff toothbrush to scrub hardscape. For driftwood with algae worked deep into crevices, a wooden skewer or cocktail stick gets into gaps a toothbrush can't reach. Do this outside the tank - the last thing you want is to release a cloud of fragments into your water column, where they'll settle and start new colonies.

Step 2: Bleach dip hardscape

For rocks, ceramic ornaments, and any hardscape you want to keep: a bleach dip at 1 part bleach to 19 parts water (roughly 5% solution) for 5-10 minutes kills Cladophora reliably. Rinse thoroughly afterwards, then soak in dechlorinated water with a double dose of water conditioner before returning pieces to the tank. Do not bleach dip driftwood - it absorbs bleach deep into the wood and can leach it back into your tank even after rinsing.

For driftwood, hydrogen peroxide (3% solution, applied directly with a syringe or spray bottle while the wood is out of the tank) is safer. Leave it for 5 minutes, rinse well, then return to tank. Repeat weekly until the algae stops regrowing.

Step 3: Replace infected soft media

This is the step most people resist, and it's why their problem keeps coming back. Sponge filter media and filter wool that's visibly colonised by Cladophora should be replaced, not cleaned. The algae works into the foam matrix at a depth you can't reach by rinsing, and fragments survive most casual cleaning routines. If you're worried about losing your bacterial colony, read up on how to cycle a fish tank - seeding a new sponge alongside the infected one for two weeks before replacing it protects your cycle.

Step 4: Liquid carbon as a suppression tool

Glutaraldehyde-based liquid carbon products (Seachem Excel being the most commonly available) can suppress Cladophora growth when dosed consistently at the recommended rate. Spot-dosing - drawing up the liquid carbon into a syringe and applying it directly to colonies with the filter turned off - is more effective than broadcast dosing alone. Leave the filter off for 10-15 minutes after spot-dosing.

Be realistic about what liquid carbon does here: it slows and damages the algae, but in an established colony it's unlikely to eradicate it on its own. Use it as a follow-up to mechanical and chemical treatment, not as a first response.

Step 5: UV sterilisers - modest help

A UV steriliser won't kill attached Cladophora colonies, but it can kill free-floating fragments before they settle and establish new growth points. If you're mid-treatment and concerned about spread, running a UV unit for a few weeks is a reasonable addition to your toolkit. It's not essential, but it's not wasted either.

What makes Cladophora different from nutrient-driven algae

Most aquarium algae problems - green water, hair algae, brown diatoms - are your tank telling you something about light, nutrients, or the nitrogen cycle. Fix the underlying condition and the algae retreats. Cladophora doesn't follow this logic. A perfectly balanced, low-nutrient, well-lit tank can sustain a Cladophora colony indefinitely once it's established, because the algae isn't opportunistically filling a niche - it was introduced and it stays.

This matters practically: don't waste time adjusting your lighting schedule or cutting back on fertilisers expecting the algae to starve out. It won't. Physical and chemical intervention is required regardless of your water parameters.

That said, good water quality and stable parameters do matter for your fish and plants throughout the treatment process. Keeping an eye on aquarium water parameters during treatment - particularly if you're spot-dosing glutaraldehyde near plants - helps you catch any stress early.

Preventing reintroduction

Once you've cleared an outbreak, prevention comes down to one discipline: quarantine everything before it enters your display tank.

Set up a simple quarantine tank - even a 20-litre tub with a sponge filter is sufficient - and run all new hardscape, plants, and décor through it for two to four weeks before transfer. Inspect moss balls specifically under good lighting before purchase. If the surface texture looks uneven or has outward-pointing stiff filaments rather than a uniform velvety pile, don't buy it or quarantine it first.

For second-hand equipment, bleach dip everything that can tolerate it, and replace anything porous that you can't reliably sterilise.

Do algae eaters help?

Mostly no, and this is one of the hobby's genuine debates. The rigid structure of Cladophora puts off most algae-eating species that readily tackle softer algae. Amano shrimp (Caridina multidentata) will occasionally pick at the surface of Cladophora mats, but they won't clear an established colony. Siamese algae eaters (Crossocheilus oblongus) are often recommended for general algae control but show limited interest in Cladophora.

Nerite snails, Florida flagfish (Jordanella floridae), and mollies are sometimes reported anecdotally to graze it, but results vary enough that you shouldn't rely on livestock as your primary treatment. They may help suppress very light surface growth as part of a broader strategy, but they won't solve a serious outbreak.