Mario, that's true that a lot of the bio load we add to our tanks is from the food we drop in for our fish. Feed light and your nitrate creep will be lower. Problem is, you nitrate is still going to creep up every day and continue to accumulate. It doesn't go away on it's own. The problem with just adding what evaporates is, compounds, minerals, etc.. are left behind when the water evaporates and will continue to build up. This will eventually shift your GH,Kh and other things to the point your pH will crash and kill your fish. As said way above, this is never a one size fits all scenario. Your water will deteriorate at a different rate then everyone else, same with the fish you keep. Water clarity means very little for water quality.