Slow down a bit. One of two things happening. Most likely, the tank is still in the middle of a cycle. Remember the cycle "wave" ammonia spike, ammonia drops, nitrites spike, nirites drop, nitrates spike. Somewhat less likely, your water supply has chloramines and affecting your ammonia readings. Huge water changes in the middle of a cycle aren't going to speed the process up. It's hurry up and test daily. Invest in the best quality kits you can get your hands on and make sure they aren't expired. If the smaller tank is that crammed, talk to the folks at that LFS and see if they'll let you keep a few fish there for a couple of weeks to alleviate the crowding.