I know that fertilizing is not the most important part and I don't put my effort only on it.
Based on the quality of your water and everything you've described about your watering habits, I think you might be a good candidate for slow release fertilizers and don't worry about mixing when watering. If you do have access to RO water or Distilled, then you can use that for the misting system only, which will prevent most deposit from forming, and keep watering with your good quality tap water.
You can use the slow release as a "baseline," assuming that your water analysis works in a range and is not necessarily going to be ever consistent. If you want to be safe you can aim for 75ppm N a week with a slow release and then adjust from there based on observation.
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