My 125 was freshwater (cichlid) and I don't have to care for it for weeks...except for water change. I first started checking the water parameters every week for like half a year and no spike of any kind, so I started checking it every 2 wks and eventually 1 month.
There were no problems with my tank for well over 7 yrs....then the big bad hurricane came and wiped out half of my tank.

I can only save half of my fishes.
I am not sure what to be careful about, I guess it's similar to saltwater...basic water parameter (pH, ammonia, nitrate, nitrite, temp). Also, it depends on what type of fish you gonna keep too. Cichlids will need trace elements (lakes) too, most tropical fishes are easy to keep. HTH.
Let us know what you (well, your daughter) guys gonna keep...*cough*marine fishes*cough*

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