One thing I found to be a problem is if the dosing solution is placed underneath the tank, and a fairly long airline goes up to the tank, there is a slight head pushing down, and no micros are dosed into the tank since the checkvalves aren't that good.
To get around that, I integrated the micro dosing with the macro powerhead dosing as drawn here:
This way, the micros are injected into the macro hose at about the same level as the dosing bottle, and the amount equals whatever the syringe doses in one turn.