The 7 cm size is standard length (SL), i.e. length from the snout to the base of the caudal fin. So you need to add 3 to 4 cm more to the total length (TL).
In my humble opinion, housing them in a 1 foot tank is just okay, the more hiding places, the better it is. They like some current in the setup, but would be tolerant of slower flow. Good level of dissolved oxygen is more important.
There is a question for you though. Are you intending to keep it together with a pair of Apistogramma spp.? You mentioned it's an Apistogramma tank.
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