Where do you have it connected? The problem with that H55 model, is that it uses a std. 3 wire fan. If it is plugged into a 4 pin header like the CPU FAN header, chances are the PWM controller on the board won't be able to slow it down. As a result, it will run at full RPM all the time. If your MB has a sys fan header that is 3 wire and/or controllable in BIOS, move the fan to it. Then set the speed accordingly.
My Corsair H60 uses a 4 wire fan (PWM). If all else fails, swap out the 3 wire rad fan for a 4 wire PWM fan and plug it into the CPU FAN header so it can be controlled like the stock cooler's fan was.
Oh, and always keep the pump running at full RPM. If it is connected to a fan header, be sure the fan header is set to run at full speed in BIOS.