After doing the math (same as you) and I also realized that for Flourish and Flourish Excel, I need to dose my 6 gal tank such tiny amounts, 0.6ml and 0.5ml, respectively, which is a royal pain to measure, since nothing around the house measures that small.
I went to Amazon and picked up some 1 ml needle-less medical syringes (like yours, but 1ml max), which made measure a LOT easier. At least, while the bottles are full. Once the levels get lower the syringe isn't going to reach anymore, and I'll have to invest in some smaller bottles just so I can reach it.
On the downside, I had to buy a box of 100, so if anyone needs a few, I have plenty of spares for cheap, LOL.