If you use the right kind of fish, maintenance is hardly required at all.
I have a pretty elaborate aquaponic system at my house with tilapia. They can tolerate seriously nasty water, they eat pretty much anything, etc. For tilapia, their only real requirement is that the water temperature be pretty high--above sixty to live, and above seventy-five (give or take a few degrees) to really grow.
Catfish are even easier--similar tolerance for muck, higher tolerance for temperature. They just get bigger.
Get a simple kit for testing pH and ammonia, check every once in a while (especially at first), and if you see a problem, fixes are easy. If the ammonia is high (constantly high, because natural spikes will occur as the nitrogen cycle develops) you should remove some fish, increase your water volume, or add more plants to your system. pH usually isn't a problem, so long as you use something chemically neutral (gravel works surprisingly well and is "less-than-dirt" cheap!).
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