Adrienne, don't worry about the Nitrate and PH swing for the time being. As for the ammonia and nitrite, the reading is ok being so low. Just give the new filter some time to kick in. Being such a big tank there should be enough bacterial on the surface area of the glass, plants, gravel and whatever you have in the tank.
No need to panic and start adding all sort of stuff into the tank. It will do more harm than good.
Patience is the key to good fish keeping.
ron