I am happy to be able to help a fellow fish keeper.
By the way, did you test ammonia? It is the first thing we need to test. Both ammonia and nitrite should be at absolute 0ppm.
Nitrate can be up to 40ppm or more without a problem.
As for the filter, I hope you have added the new filter without removing the old one. If you did, all the good bacteria are gone once you removed the old filter. It is recommended to let both filters run together for 3 to 4 weeks before removing the old filter if you ever want to remove the old filter. It is also fine to keep the old filter after the 3 to 4 weeks if you wish.
