Plant Melt From Bottom

[Istehad]

Hey guys. New member here. So I needed some help with my planted tank. I am having trouble in keeping plants alive because whenever I try a stem plant to grow they always melt . Its not like the "leaf melt" but the plant stem melt from bottom where the roots form. No matter what the stem melts from the bottom . I have sand substrate and its coarse sand and using root tabs but the plants seem to be healthy for a few weeks then it just floats over with no leaves no roots. But my dwarf sag. , val, sword plant does well. Its only the stem plants. So what should I do?

[knee]

Maybe the bottom part isn’t getting enough light? I’ve experienced plants losing leaves on the bottom part of the stem because I didn’t have the light strong enough.