kribs are really easy to breed, if they dont, try separating them for a bit and feed them some good proteins and wait till the female is plump, then bring the male back in...
a cave too..they breed in caves
You can also try doing a 25%water change and going up 1 to 2 degrees on the temp. This throws mine into spawning. I have also found that by adding another female to the tank produces quick spawning from the frist pair.
Mine bread all on their own, all I did was do a few water changes in a week. I went to clean the tank one day and found eggs in a little cubby hole. My other pair I didn't even realize was a pair and after I got back from a trip I saw th substrate moving and looked and saw babies and really protective parents too.