I have never spawned Columbians but here is a method I have used for many other tetras.......
Tank 24"x8"x8" prepared...temp 78-80...a carpet thicket of plants (artificial is fine)...pick a fat female and colourful male...after a few days of seperation, introduce the pair to each other 2 hours before dark...this gives them enough time to settle in and say hello!..within 2 hrs of dawn the next morning the pair should spawn.....
Mostly I have let the pairs stay in darkness until 'dawn' suits me (ie. when I am home from work)...they usually start within the first 2 hours and the whole thing lasts for about 2 hours...the pair need to be taken out when they are finished spawning...works far more often than it fails!!!