1) Clown loach - mine have just started to do the "pretending to
be dead" act. I have read this is typical loach behaviour, but
is it because they are unhappy/happy/growing up/whatever?

As near as I can figure, it's because they are INSANE. Generally
with my guys it seems to precede bursts of manic activity, so
maybe it's like naptime in nursery school?