If you get a scale, make sure it will measure milligrams accurately (0.001 g). Personally, I find that scales (especially the accurate ones that need to be sheltered from air gusts) are very annoying to use on a repeated basis. I would suggest either making stock solutions (use the scale for accuracy) that you dose out with a syringe, or using the scale to find a scoop that will measure out each amount you want to dose. The second method may be difficult with nano tanks.
What I did, since I did not feel like carrying bags of powder to work, was use wet's calculator to first give me a mg amount for each fertilizer. Then I guessed at what fraction of a teaspoon would approximate that amount, adjusting up or down as necessary. I got a set of very tiny measuring spoons from Pure Bulk, and now I can scoop out what I need each day quickly and painlessly.