Condensate not draining from a steam coil

The steam coil in a Desiccant dehumidifier system freezes due to the condensate not adequately draining. The freezing occurs in the 4th tube up. The traps have been changed, the slope has been verified, the condensate drains were lowered to create more vertical distance, the vents were checked. There appears to be a calcium build-up in the tubes and that is being investigated further.



Is calcium strictly a water treatment issue? What works best to clean the tubes of the coil?