Rudy:can anyone guide me how to built a simplest sump refugium for my saltwater aquarium??
Welcome to ReefForum.com Rudy!
What size of Refugium are you looking for? 10gal, 20gal, 55gal? Depending on size, the bigger gives you more choices of layout and a 10gallon tank without an overflow would require a hang-on refugium for a simple setup.
Here is a good 20gal layout (I would remove the foam). Click Here.
135g Main Tank/ 125g Frag tank with 55g sump.