Melting Banana

Hi group, I've got a question about the little banana plant. Mine is
developing new leaves, but they melt and rot off before they have a
chance to get much bigger than a silver dollar (coin). This just
started about 2 weeks ago. I've had it for a few months and it has
grown several larger leaves in the past.

55 g tank
fully planted
pH 6.8
temp 80F
dosing with KN03, KCI and traces daily

All the rest of the plants are doing great. Bacopa, Ludwigia, crypts,
water sprite, wisteria, java fern and moss.

thanks for any suggestions/tips,
steve