I am new to the forum so thank allof you for doing what yoi do to help people like me. And so here you go. I have an aquarium that measures 6' long X 18" wide X 21" tall. Im not sure how to measure the capacity. I have had it set up for years as a freshwater aquarium. My last freshwater fish has oassed and moved on to the big lake in the sky. I have been waiting a while to do this so i want to do it right. Can anyone guide me in what i need to set my tank up for saltwater? Pumps, skimmer etc. Look forward to hearing from you and thank you in advance.