Collocations for slack - adj.

be, feel, look, seem | become, go
Let the reins go slack.

leave sth
Leave the thread slightly slack to allow for movement.

very | completely
Some of the ropes were completely slack.

a bit, fairly, slightly

be, seem | become | remain
The antiques business remained slack.

extremely, very | a bit, fairly, pretty, rather
This season has been pretty slack for local hotels so far.

be | become

very | a bit, rather

in
She knew she had been very slack in her church attendance recently.