Dry powder. On their website they have several options and you can send in your water, if tap, for testing and they recommend based on that if you don't use RO.
It's a pretty simple Part A, epsom salt, Part B. The Part A is the only real unique one. The epsom salt, well, easy and cheap. The Part B is just calcium nitrate.
They have a few other products like clone/seedling starter, bloom booster, "finish", and something called ultraviolet. Lots of guides on YT from a guy called Green Gene.