Broomer:
Got it from <a href="http://www.reef-aquarium.com/" target="_blank">www.reef-aquarium.com</a> They sell refurbished peristaltic dosing pumps (the ones they use in hospitals). I clipped the wire to the audio alarm since I'd rather not know I've run out of kalk at 3:00 amm but that was my only modification, and it took 10 minutes to setup.
If you want it on a timer or a float valve, you would have to be creative in re-wiring the switch and built in batttery, but it works great as is if you dose 24/7.