Commercially grown plants are cultivated “emersed” rather than “submerged”. This way the plants can easily get their carbon requirement from atmospheric CO2
. They can be grown quicker which makes the operation much more commercially viable. You take that plant, put it in your aquarium, cut off its source of CO2
and the plant goes into survival mode. It starts to use up its stored carbon and the leafs melt. You may lose all your original growth to melt but new leafs will have a structure more suited to its new environment and get its carbon from the water. Plant melt is a normal stage in aquarium plant growth. To judge the health of a plant look for new growth rather than what might be happening to the original growth, and judge it over extended periods of time.