I've decided to get an RO unit from RO-Man.com and all the associated bits. Looking at a 75 gallon per day jobbie without a DI unit. I'm going to be using around 25% tap water to 75% RO water to give me a KH of roughly 4. By doing this, will I need to add any minerals back into the water? Or will the tap water provide sufficient quantity of minerals for a healthy tank? I measured a KH of 15 out the tap last night and have seachem onyx sand which buffers slightly as well so I calculate 3.75.