How to correctly make chocolate bars? I was hoping someone would be able to help please?

My brother has started making chocolate bars, we are using cargill 30% cocoa chocolate- we fill the prefamac chocolate machine with approx 7kg and leave the chocolate to melt for about 6 hours at 41-45 degrees. Once melted, we bring the temperature at 30-31 degrees and seed this chocolate and maintain the temperature- we allow the wheel to consistently mix the chocolate. As we fill our chocolate bar moulds we keep topping off the chocolate in the machine with more chocolate which we melt in the microwave at 30-31 degrees.

The issue we are having is that that the chocolate- once we eat it, it won't melt in our mouths like other chocolates melt when you let them sit in your mouth.

Are we doing something wrong? How can we make the chocolate so it is the type which can melt when sitting in ones mouth?
The secret ingredient of all Chocolatiers: cocoa butter...

I use a different brand of chocolate (Callebaut) so I don't need to add any cocoa butter, but as I've never used your brand before, directing you to their product line.

Be careful, because too much cocoa butter will make the chocolate melt in your hands and in your mouth! ;-) 

I would start off with 10% of total weight of additional cocoa butter and increase if needed (start with small batches as 7Kg is a lot of chocolate!)