The ceramic noodles are just ceramic rings that look sorta like a thick ring you would wear on your finger, only smaller. They have a porous serface area that tends to hold bacteria better than many objects. There are better things on the market for bio housing, but these were about $7 and there were too many to fit in the HOT basket. I still have about 1/4 left over for other use. I bought them from Petsmart....probably Proquatics brand, but they also had Fluval. You can buy them from many places in many brand names, and most canister filters have their own brands. I think I'm going to try the bio-stars next.
I really have had no problems with the HOT holding capacity for media. I know alot of people like to overstock their tanks and maybe they do need more room for bacteria, but I don't overstock and I've been fine. The Magnum HOT I have was a hand-me-down, and I have thought about buying another with the micron filters. Nice cleanup duty.