pH is fairly well correlated with kH. You might want to have whoever's feeding add a little baking soda to maintain pH. Mine starts at 8.1 but I have to add 1.5-2.5 g of bicarbonate everyday or it will drop below 7 within 1-2 weeks. At my previous place, pH was ~8.3 but wouldn't budge even if I went weeks without a water change.
I also agree that you should take it easy when you return. You don't want to do a huge water change or let them pig out. Ease back into things.