Not necessarily hard, it's just that
a) you need to have a big tank for them, 55-60 gallon minimum,
b) you need to keep them in a shoal of five to six,
c) you have to be very careful with tankmates as they are sensitive and peaceful fish,
d) you need some high temperature, I'd say around 82-84 degrees F, and
e) you have to be extremely important on water quality, as in stable pH (not too alkaline like 8.5), no ammonia, no nitrites, and don't let the nitrates go over 20 ppm.
That's all there is to them I'd think.