I have a minimal medium where casein sodium salt needs to be added. As it's a medium to grow bacteria and to avoid contamination I have been trying to prepare a solution separately and filter sterilize it before adding to my media. The main problem is with 0,45 and 0,22 filters barely 2 mL can pass before the filter clogs up. anyone having the same experience? how do you filter sterilize it or do you just directly add the powder.