If it is like other peristaltic pumps I have used, it will allow you to control both the rate and duration and which pump head is active. The rate you are seeing is probably the max dosing rate. I was going to suggest you give them a call and then realized they are in Germany. Try emailing them:

info@aqua-medic.de

Your other source of info would be one of the online distributors. Give one of them a call and see if you can get more info.