I think you maybe misread. But the PUMP (AIO) Should be plugged into the CPU FAN Header on the MOBO then you connnect the splitter cables to the cpu fans on the radiator, Basically there should be nothing connected to Pump Header on the MOBO in the corsair setup. Then your CPU RPM should be correct and control both fans correctly via bios.
However in my experience the best way to actually control the pump is the via the iCue software with the Corsair Series of AIO's its one of the reason's i swapped the EK AIO minus better cooling but because its less software and you can control both fans & pump via Bios.
Also this certainly isn't the correct thread to be discussing this issue. I feel like we are spamming a thread way off topic here.
@Mussels will need to move/clean the thread up afterwards.