aquatraders.com is where i got the overflow, pump, and protein skimmer for less than 75$. I have not found a site that explains everything very well, so I can tell you what I know. A refugium employes a deep sand bed (about 4" or more) where anaerobic bacteria lives in the stagnate conditions at the bottom of the sand (it converts nitrate to nitrogen gas that easily removes itself through gas exchange at the surface), I use a 2" layer of crushed coral, then a 2" layer of live sand. Also in the fuge, I employ macroalgae, it helps soak up excess nutrients, provides perfect living conditions for pods, and also supplies a harvesting area for fresh food for tangs. As far as overflowing the sump, as long as you only put enough water in the sump to get it to a level that you want it will not overflow. The pump will pump an amount into the tank, and then the overflow will take the same amount out. Google search and maybe you can get more help. If you look at that 350$ sump, you can get an idea of how your setup should look. I built one for a friend, and also for a guy that employed me to set up a tank for him, and trust me, practice makes perfect