Gaboon - I don't use it (never have). But, I have used the SeaChem ReefBuilder....
I can only think that you mix it up EXACTLY the same way you mix up other kalkwasser.... The difference being, I think that the SeaChem product is a different Calcium compound.... not calcium hydroxide...
Perhaps post the actual calcium compound and we can assist better...
Ok let me try do this and not confuse you or me to much.
You need to connect one of the tubes from the top of the reactor to your RO top up pump. (I am assuming you do have a top up). The one to connect to is the tube that is not in the center and goes right to the bottom of the reaction chamber.
I put a one way on this as it will siphon back if your top up is lower than the reactor which mine is.
The tube that is in the center of the reaction chamber is the one that goes to your tank/sump. There should be a valve on this to help you control the flow. Put this into your return chamber in the sump where the float switch is for the return pump.
What will happen now is that as your tank needs top up, water from the top up is pushed to the bottom of the reaction chamber and forces water out the top into the tank.
Not sure what size unit you have but put about half a cup of kalk in the reactor and then let it fill with RO. You should set the Kalk stirrer on a timer to mix every 3 to 4 hours. The pump will come on and mix up the kalk for you. You will have a milky mix in the bottom half of the ractor and then clear in the top.
I hope that makes sense, if not I will try take a few pics for you to try and explain it a little better.
By the way, some people only let the return pump kalk back at night to try control PH. I just let mine top up when it wants to as I only have a nano and use abot 4 liters a week so it is only dumping a small amount of kalk at a time.