Do I really need to buy?

[Animal-Chin]

If all you are going to have is fish and some soft coral you don't need any type of dosing or reacting at all. Out of that list the only thin I wouldn't live without is and auto top off. They are $100 and you don't have to worry about evaporation. My 125 gallon tank goes through 2 gallons of water a day, I don't want to have to worry about that. I go away a lot too, its nice to put down 15 gallons of fresh water and take off and not have to worry.