My fish are years old and I NEVER feed them!!
Babying your fish, in unatural environments, is like keeping humans on respirators, and then wondering why they die when there is a brown out.
Keep the right water temperatures.
(Make sure there is always a natural wide changing of temps fluctuating around its ideal temp).
Keep fresh air flow over the top to help oxygenate the tank.
Have good oxygen and food producing plants and algae. The water and sides should always be a bit green. But not so much you can see inside anymore. Also the plants will use the fish waste (recycling the nutrients).
Add fresh, chemical free water, as this evaporates.
Keep an eye on your fish. Daily if possible. Make a bond. So it knows you care.
But follow this, and they will grow healthy and strong (as they naturally do, in nature), even if you cant go home for months.