Its not that crystals are "hard". They just are much more particular to water conditions like ph, temp, and hardness. The cherries, snowballs, and yellows are all very accepting of a wide range of pH and breed readily. The crystals don't always breed in pH above 7 or in temps above 74. They prefer cooler, softer water. I *seem* to be having success with my source water but only time will tell. I am considering altering my chemistry to suit them and some tiger shrimp I am getting in this week. The choice is yours. The crystals are more expensive than the cherries by far. If you decided to have cherries and then add crystals, they can be housed together with no issues.