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.