Answer:
Take the battery (temporarily) out of the toy truck, using the screwdriver that is in the kitchen drawer.
Feeding the Fish
Turn on the TV and climb the antenna, where you will get a static charge. Now you can jump to the left and you will stick to the green balloon. When it carries you to the picture frames, jump off and down to the fish food shelf. Feed the fish, and turn off the aerator (filter) so you can swim down in the tank. The key to C.J.'s diary is in the little treasure chest.