A word on how I run zone spells like Spirit Guardians (it nerfs them a bit...since you don't have damaging casters it probably benefits you overall):
Zone damage takes place as soon as the zone appears or as soon as a character enters it (or it moves over them). You can only take damage from a zone spell once per round. So if you take damage from it, you can't take it again until the start of the caster's next turn.
So the Monitor and Whip will not take damage again until after the start of Ploop's next turn.