You probably would not want to run it off, of the float switch. Those things are known to clog when used with Kalk. My solution is, a solinoid with 2 float switch if you are going to run it off a R.O system, or just connect it in-line with the top-off system of your choice.
As far as kalk getting to the top, with the model that Tim has with a whole bag in it, it didn't even get more than 3/4 of the way up. For a 700g, I would probably use a 3 footer, because the pump would be on for a little longer time in your system. Plus it would hold more saturated water for a tank that size. So when your top-off is dosing, it would push the saturated water out into your tank. Allowing for the new water to get saturated. Most small units will push all of there saturated water out, plus push alot of unsaturated water out as well. That happens because the evaporation requirment is greater that the volume of saturated water in the Kalk reactor. That is why I said 3 foot for your system, because I do not think that it would evaporate more water than that 3 footer can hold.(maybe) It would be real hard to get Kalk out of a 3 footer. How much evaporation does your tank go through about 3-4 gallons a day.
Aquadoc
Mike Hummel
\"A happy acro, is a fed acro.\"