make sure the top off is fresh water, you know your tank better than anyone else. So what are your system problems, how fast does algea take over your tank, do you have a cyno issue? You probally should consider cutting back on feeding when you are away annd maybe decreasing your lighting schedule.
I just got back from a 2 1/2 week vacation, all was well but there were issues. First I left a day by day callender for the person maintaining my tank to follow and also left notes for worse case senarios. The worst thing I list was a chiller failure. And of course 5 days into the trip the chiller failed. An hour phone call enabled me to remove the chiller from my system and luckly it was just the in line fuse and everything was back in business.
The other thing I did not realize till I returned was that I had plugged my artinic lights into a timer that was permenantly on, and this lead to some algea issues. NOTE to adjust your times 1 or 2 days before your leave to make sure they function correctly.