I have had these mangroves for about 6 months and they have grown about 4 inches since I got them and they have been doing great. But, all of a sudden they are starting to die off. The leaves turn brown and fall off and then the stem turns brown and withers. Some of them still look good, but I'm worried they will die soon too. They have a lot of light, and I spray them every few days with fresh water. I haven't made any changes to the aquarium. Does anyone know what could be going on? I included some pictures.

