A plant suddenly melting?

[KiwiWillow]

Can anyone identify what’s happening? This is a stable tank and everything is currently ticking along nicely. Except today I noticed the plant at the front right corner seems to have a white coating and leaves are melting away. It’s been in this corner for over two years. About 9 months ago it melted away (had been a very thick clump). I don’t know if the white coating happened that time. A few stray plants regrew to about twice what I am seeing there today ( The tank is in my workplace, so I don’t see it every day)

 

[dcutl002]

I think that is an Aponogeton species and may be going into a dormant period. Aponogeton ulvaceus | Aquarium Plant Profiles Forum

 

[KiwiWillow]

Thanks, and that looks like a lovely plant. I couldn’t remember planting a bulb so I went hunting for a name. It’s a humble old cryptocoryne, which I guess explains the melting. I can’t figure out why though. Obviously some sort of parameter change that everything else took no notice of.

 

[ruud]

The white coating could be calcium. This can happen if light is strong, dissolved CO2 is low and the water contains enough bicarbonate and calcium (GH and KH), certain plant species then turn to bicarbonates as the carbon source.

Doesn't explain the melting, but softer water and softer light makes conditions less demanding for most if not all aquarium plants. Melting is typically caused by a strong environmental change; perhaps what caused the calcification also: an even lower than "normal" CO2 concentration.