Thanks Jack,
I'd thought that was a simple typo. Now I just need to figure out in inches what size tubing I need. It's probably the smallest they carry for a 7014-21 head.
Brian,
Sorry it's in Dutch, but the pictures should explain enough.
http://www.home.zonnet.nl/rsetteur/aquarium/karel/doseer_pmp/index_doseer.htm
I don't know about Jack's pump, but mine is DC. So is the one on that ebay link likely. So it won't work without the controller. If you can find one that's not variable speed, it'll be fine since you don't really need it given you have an AC. As far as dosing Mg at the same time. If you can get 3 heads cheaply, it should be easy enough either with different sized tubing or diluting the Mg container. Just make sure you're getting heads that will connect to each other. I've seen at least 3 types. Square, slotted, and some that will not connect to additional heads. FWIW, you could setup another head to dose for almost anything you regularly add to your tank with an extra container, a little math, and dilution.
To explain what I mean, and why I like the idea of getting an expandable dosing setup here's an example.
Say you'll be dosing 5 gallons of 2 part every 2 weeks between refills. I think the used ratio of mag to ca is 1:5. So you'd put 1 gallon of the Mg part in a third 5 gallon bucket and fill it the rest of the way with just RO/DI. Then say you want to dose trace elements like SeaChem's Reef Plus and Reef Trace or Tropic Marin's K and A elements. You'd just take the recommended dose, something like 1ml or 5ml per 50g and calc what you'd add per day then multiply that by however many days you have enough 2part for (14 in this example). I think TM is 2ml per 50g max per day, so roughly 10ml max per day in your new system, so you'd add 140ml of each trace elements to a 4th and 5th bucket and then fill them with RO/DI.
This goes for almost anything you add to your tank, so you only have to deal with it once every X days rather than daily. I'm not saying to worry about setting it up now, just something to think about when getting a dosing pump.