It looks like your not wetting all the soil,maybe they need a good soaking,be carefull with the one in the 5g bucket if it does not have drainage holes it really should along with all containers so excess water can drain out.

Maybe too much water. Do those plastic barrels have holes in the bottom? If not, the roots might be getting swamped. If that's the case, I'd recomend you cut some holes in the bottom and put a secondary tray underneith to protect your floors.

Don't water for a bit and let that mess clear itself out.

both have holes for drainage

Looks like too much water to me. Let that soil dry out a bit.
Bananas dont like alot of water until its hot outside.
Stick your finger in the soil,
If the soil is wet or damp don't water.
Also the soil your using might be a bit heavy.
I mix my soil with alot of perlite to keep it from being to
heavy. I also mix in peat moss.
Good luck, hope this helps.

Try giving it a potassium rich fertilizer

Here is a link that might be useful: Jeremy- Moths and Butterflies