with Plantladylin. Also, please remove the layer of rocks from the bottom of your pot. Instead of aiding with drainage, it actually hampers it, keeping the medium too damp too long. Thus causes the roots to rot from the bottom upwards. You also mentioned placing it in a larger pot. Did it need to be placed in a larger pot? It sounds like you made a lot of changes in a short period of time, causing stress to the plant each time.
I see that your pot has a saucer, be sure that you empty it so that there is no standing water, otherwise the roots will starve from lack of oxygen. One other thing, these plants need high humidity. So, placing it outside, will do it a lot of good. Happy growing with your new maranta/ctenanthe. It is a very pretty plant.