Need Advice on Top off System Please!

[mark]

Not using Kalk for calcium (have Ca reactor) but do have a ATO. Can be as simple as you figure, a mechanical float valve in your sump and a reservoir above. The reservoir can be directly above the sump or even in another room.

Kalk Reactor are simple and lots of DIY designs out there but basically a resealable container, pump for stirring and a timer. To have a kalk reactor, could just insert between your fresh water reservoir and the float. Since using gravity, the reactor could sit on the floor beside your sump, reservoir again wherever just as long as higher.

Before getting to involved into reactors though, might want to get a ATO set up first and monitor to determine your Ca needs.

Lots of reading on Canreef if you do a search for "Kalk Reactor", might even find a few FS or at least pictures for ideas.