I currently have a 75 gallon tank similar to you, and I use the Coralife Pure-Flo II that does 50gpd. It has the DI unit and has nothing short of exceeded all of my expectations. I used to use just plain tap water, and finally I saved and purchased this R/O unit. Another plus, is the Pure-Flo II is often less expensive than competing models, but with the same if not better performance. This is what I would recommend to you. Good luck!