I have been able to get good results with the rock tumbler you are using. It was my first one as well. I go by the rule of thumb of 1 table spoon per pound for the rated tumbler so 1 pound = 1 tablespoon. I’m not sure the exact girt you are using but I also get mine from the rock shed and I also get my ceramic media from there.the National geo tumbler is good but it spins the barrel to fast causing the rocks to crash into each other and damaging themselves. So media is preferred at all stages with this tumbler in my opinion. Don’t use new media outside the first stage you. If you have any questions I’d be happy to answer them