I wouldn't use any fertilizer in the plants. Sometimes chams eat the dirt, even if you put rocks on top of it. For some reason my ladies like to snoop around in the pots. No, they aren't gravid, just like to play in the dirt. LOL
No way! Besides the obvious "what if the cham eats some dirt", there's an off chance that if your cham eats leaves it could it in their system. Get some fish emulsion or bat guano if they needs a boost.