reomoving teh bioballs is a great idea, however, your water parameters say all is well now. I would attribute the zero nitrate to your fuge ans well. The filter pad also works as mechanical filtration. I still use one just to catch the big chunck of detritus when I do water changes. Otherwise, it take it out. Shop around for rubble. You may be able to find a LFS
that will give it to you. Otherwise, it is not too expensive. As mentioned, do not remove all of the bioballs at once. Do about 1/4 of them every week or so until they are gone. You also may need to raise the water level in your sump so the rubble is completely covered.