Can't seem to get the medium right. Help!

[Kasiopea]

Hi guys,
I made a set of jars a good while back and everything went by the book. But since then I've been trying to prepare another flask batch, three times now to no success. What seems to be happening is I can't get the proportions right and the medium does not gel correctly. First failed attempt, the medium seemed too wet and separated, the charcoal dust settling on the bottom, and if you shook the flask the media would just swoosh around as it never firmed. I though it was an old pack of media, and ordered fresh stuff. Well the same keeps happening to me over again. The media seems to not gel well and then, the next morning there is some extra liquid separation on the top. The longer it sits, it seems to get more soft, fall apart in chunks if you tilt the flask. First time I got grayish gel on top and charcoal settled on the bottom. Second time media was black throughout but had water later on top and broke appart. Third time it all completely separated into water, and media settled on bottom.
Here are my steps:
1.Add half pack of the black medium (sold in silver packets on eBay) to 500ml water. Gradually, mixing well.
2.Bring to boil for a couple minutes steering then pour into flasks.
3.Close flask and sterilize in a boiling pot of water for 30min. I add enough water to cover 3/4 of the up right standing flask at boiling and make sure the lids are above water so no water leaks in.
What am I doing wrong? I also hear that people prepare media in a microwave? how does that work? how long do you nuke it to sterilize?