Category: Troubleshooting

Black beard algae is the dark, bristly growth that grips plant edges, wood and equipment in planted tanks. It is a red alga, sold and discussed under the names black beard or brush algae. It is stubborn rather than dangerous, and it almost always points to something specific being off in the tank.

What it actually is

Black beard algae covers species in the genera Audouinella and Rhodochorton. It attaches hard to surfaces rather than drifting, which is why wiping does so little and why it tends to colonise the slowest-growing leaves first. Older Anubias leaves are a classic site.

Why you have it

There are three well-documented causes, and they point at different tanks.

• Organic pollution: in tanks with a heavy fish stock and few or no plants, the black variant is common. The cause there is high organic pollution from overfeeding combined with too few water changes.
• CO2 shortage: where CO2 is short, these algae can take the carbon they need from hydrogen carbonate, and they do it far more easily than higher aquatic plants can. That is the mechanism behind the usual advice that unstable or insufficient CO2 brings on black beard algae. Your plants stall, the algae does not.
• Nutrient imbalance: in properly planted tanks it often appears when micronutrients are out of balance, iron in particular.

Work out which tank you have before you treat anything. A heavily stocked, lightly planted tank has an organic waste problem. A high-tech planted tank creeping with it has a carbon or nutrient problem.

Getting rid of it

Liquid carbon is the usual first move. Dose per the manufacturer’s instructions and the algae should turn whitish or pink within a few days, which is the sign it is dying rather than a trick of the light.

If that does not clear it, treat the affected spots directly rather than the whole tank. Spot dosing an algicide or hydrogen peroxide onto the growth is the targeted version of the same approach, and it works on patches that whole-tank dosing leaves behind.

Neither is a fix on its own. If the underlying cause is still there, it comes back. Sort the feeding and water changes, or stabilise the CO2, and the treatment gets to stay ahead of it.

---

Black beard algae questions

Is black beard algae harmful to fish?

No. It does not harm fish or shrimp. The damage it does is to plants, by covering leaves and blocking the light they need, and to your patience.

Why does black beard algae keep coming back?

Because treating the growth does nothing about the cause. If the tank still has excess organic waste, unstable CO2 or a micronutrient imbalance, new growth follows the old. Fix the condition first and treat second.

Should I throw away plants covered in black beard algae?

Usually not. Badly affected old leaves are worth removing, since slow-growing plants rarely recover a heavily colonised leaf, but the plant itself normally recovers once conditions improve and it pushes new growth.

Aquarium plant melt is when leaves collapse, go translucent and fall apart shortly after a plant goes into a new tank. It looks like the plant is dying and usually it is not. Melt is a transition response, and the plant regrows leaves suited to the conditions it now finds itself in.

What triggers it

Sudden changes of environment. Moving between tanks is exactly that, and most aquarium plants are grown emersed at the nursery, out of water, then submerged when they reach you. The leaves that grew in air are not the leaves the plant needs underwater, so it discards them and starts again.

Cryptocoryne species are the classic case, to the point that the phenomenon is often just called crypt melt. Bucephalandra does the same thing on its first transition, and it is normal in both.

The one mistake that kills the plant

Digging it up.

The roots are what regrow the plant, and they are usually fine while the leaves are falling apart. Pulling a melting Cryptocoryne wendtii out to inspect it, or moving it somewhere it might be happier, removes the only part that was going to recover. Leave it alone and it comes back.

The same applies to rhizome plants, where the rhizome rather than the roots carries the plant through. Keep it attached to its wood or rock and wait.

What to actually do

• Remove the dead leaves. They will rot otherwise and add to the organic load, which invites algae.
• Leave the roots and rhizome in place. This is the whole trick.
• Keep conditions stable. Melt is caused by change, so more change makes it worse.
• Wait. Slow-growing plants recover over weeks rather than days.

When it is not melt

Melt happens shortly after planting and affects the existing leaves while new growth appears. If an established plant starts declining months in, that is a different problem and the place to look is light, nutrients or CO2 rather than transition.

---

Questions about melting plants

How long does plant melt last?

It depends on the species and how different the new conditions are. Slow growers such as Cryptocoryne and Bucephalandra recover over several weeks. Stable conditions do more for recovery than any intervention.

Should I remove a melting plant from the tank?

No. Removing it is the most reliable way to turn a temporary setback into a dead plant. Take off the dead leaves and leave the roots where they are.

Can you prevent plant melt?

Not reliably, because it is a response to the change itself. Buying plants already grown submerged reduces it, and keeping your parameters steady after planting helps, but with Cryptocoryne you should simply expect it.