I've just changed from a Fluval 4Plus internal to a TetraTec EX700 external. The Fluval did a fabulous job on my 4ft tank for the last 3 years, but I'd heard so many outstanding reviews for the TetraTec externals that I thought it was time to change. I bought mine on the way to work last Thursday night. Got home Friday morning and had it running in my tank within 20 minutes, absolute dream to set up. I had good quality, clear water before, but by Sunday the water looked absolutely sensational ( I also bought an Arcadia 2x38w overtank luminaire) and the difference in water clarity is unbelievable. You need an external filter. One word of warning, though; measure the height of the cupboard space where the filter will go. The 700 is rather tall and fits into my undertank cupboard with 4mm to spare!!. But I'm so glad I finally got one. Your fish will love you for it.