Kalk and Top up Dosing Pump for very low volumes ??

[Fish]

Hi all,
I am currently using a Kent Aquadose (2.5) to add Kalk and top up evaporation. My nano only loses 1/2gal (2litres) per day and because of the very slow drip rate, the end of the tubing usually gets plugged up with kalk buildup after a day or so.
Is there a mechanical dosing pump that anyone is familiar with that could handle a low flow like this? I think that the pressure of a pump would overcome (or prevent) any calcium buildup at the end of the tubing. It would also allow me to pump from a larger resivoir than the 2.5gal ontainer I am currently using.

Thanks for your help.

- Chad