I keep a pair, they are a mated pair but haven't managed to get past the egg laying stage yet.
To find a pair you need 1 male and 3 or more females, once they pair up you rehome the remaining females. Kribs are very feisty and need a lot of 'breathing space' in a large-ish tank with lots of nooks and crannies they will conten themselves. However you need dither fish. These can be tetras, barbs, whatever, just something for them to chase off, if they don't have them then the male will be too sore on the female and maybe end up killing her.
Problem - 20G tall can't support 4+kribs to find a pair, a mated pair don't have a lot of room in your 20G when it comes to floor space.
Result - In my opinion, combined with experience a pair of kribs just aren't suitable for your style of tank
My therapist says I need a bigger tank . . . . .