I am currently maintaining the rat heart cell-line H9C2. I am using DMEM supplemented with 2mM Glutamine, 10% FCS and Pen/Strep. I find that they grow very slowly. I also find alot of debris floating around a day after splitting them or ~three days after changing the media. I don't think that it's contamination because a microbe would have fully blossomed by 3 days. Are my doing something wrong? Does anyone else have the same problems with them?