http://www.tunze.com/fileadmin/gebra...x9010.8888.pdf

hope this link helps. Ensure you check the set up of the filter as they are different for in sump and also for hanging inside the tank. In one set up it can be affected by extream currents within the system or because its still in its break-in period. Ensure you have all the parts, and also that the tube for air intake is not kinked. The knob turns to also help with foam level and thickness adjustments. I think your bioload is kinda low also for the tank even though its 3 tangs I believe you have.