The ph in my tank bottoms out, it never seems to stabilize what can i do besides adding more baking soda?

i'm having problems with ammonia levels and ph bottoming out. despite water changes, i haven't fed my fish in almost a week. they'll either die of starvation or ammonia toxicity or ph. i'm ready to give up and give them all away. 1 large lionhead, 3 small lionhead 1 small oranda 3 cory cats in a 55 gal tank.