i used to have 4..
2 died when one day my whole aquarium was polluted - all my fishes all die heart ache then...............
then i added another 2 - notorious fish mafia..
why? they always go bully other fishes around them....
i called them engineer too because they love to dig and transfer ..
i used to put landscape sand.....1 week later you can see one side heavy sand covered because they will take their time to suck the sand and ptooi on the side of the aquarium like mountain....
i seen them kiss before - that's lovely hahaa.... especially when they have sharp mouth