I just noticed from your pictures that all the pots are sitting in saucers... I don't think it's a good idea, as the pots do not have any lateral holes, and the drainage at the bottom are blocked, meaning no air circulation through the medium and around the roots. Either lift the pots on a layer of large pebbles, or put them on a kind of rack or mesh where the bottom is completely clear.
As for the crown rot, you have to follow what susan said above.
Cheers
Eric