Hey, noobie here, I'm about to start planning for a 75 gallon tank, and I'm trying to do everything right, regardless of cost to ensure the health of my future fish/invetebrates, I was wondering if anyone had a good recommendation for a RO/DI unit? Also is there a huge different between a 3 and 4 stage unit? What are the advantages of a RO/DI unit over the tap water filters that I see advertised on liveaquaria. Also I am probably going to invest in a refractometer and electric PH monitor, anyone have any good recommendations for these products as well? Lastly what type of test kits have been shown to be accurate for ammonia, nitrite. nitrate, hardness, calcium testing? I know its a lot of questions, but I really could use the advice, thanks