Then there's work, and of cause the aquarium at home with only enough RO water prepared for the week. Not having any one with the knowledge of adding supplements, let alone testing/checking them. Having a simple reef system that i manage with no gadget's does have it's drawbacks.
I think i got home in the nick of time. an immediate water change and preparation and replenishment of RO to dilute the increasing salinity due to evaporation,. The corals didn't look too good my Magnesium and Alkalinity had dropped but not too much.
So Please make sure when you go away you know exactly how much supplements are required, Mix them up ready, and then double it to cover any eventualities. Oh and make a note for the baby sitter of what you want them to do exactly with labeled supplements. Then enjoy your holiday and come back to the thriving reef you left.