One thing to keep in mind concerning chains is that they are allowed
by law to contain a lot more solder than in other type of jewelry and
most solders are not plumb.
For example platinum chains are stamped PT but are, when assayed,
around 85% platinum. Any other platinum product such as a ring
wouldn’t even be able to be stamped PT. Gold chains while not
necessarily lower in karat as platinum chains are, still are allowed
by law to contain a lot more solder than any other gold product. The
reason for this allowance by the law is that most chains are made
from wire with solder cores. However, these cores can become exposed
through the manufacturing process and are then attacked by chemicals
that don’t normally react to the gold alloy.
This is in all probability why the chains are crumbling. You need to
find a detergent/chemical that will not damage the solder in the
chain. I use Simple Green and have never experienced a problem.