They make their way past the return pump and also crawl up the plumbing to the tank, believe it or not. [smilie=lol.gif] Biggest thing with keeping a mandarin is having a healty amount to start with in the main tank and by also having a predator free area like a fuge so they can replicate. Mandarin's eat constantly and will wipe out the pod's in a relatively new tank really quick(as in a week). My suggestion is to get the ORA mandarin's if you do not have a mature tank/fuge as they are already trained to eat pellet's. They cost a bit more but not as much as trying to buy bottles of copepod's trying to keep the mandarin alive as some do.
Cheers,