Pandas aren’t very hardy. I would steer clear of them. Your tank is overstocked and will continue having nitrate problems until it really gets established. Mine took about 9 months because of the large size of my fish. Keep up the large water changes. I even had to do a mid-week one for a couple of months.
Yes, seems like constant water changes is on the cards for me looking at the Nitrite and Nitrate today.