>>> the max size in an aquarium is 3".
It's more wrong then that! There are at least 2 members here, me included, that have these at 150mm/6". They are not overly aggressive, but should not be kept with very small fish. Should be kept in groups of at least 3 fish, so a suitably sized tank is necessary.
They are scaleless, so there should not be salt in the tank and if medicating, be sure to use medications which are suitable for loaches, many dye based preparations will poison them.
They appreciate a lot of caves, holes and other hiding places, the more hiding places they have, the safer they feel so perversly, the less they hide. They will eat pretty much anything, sinking pellets/wafers, frozen blood worm etc. variety as always is the key to healthy nutrition.