The thing is that if the temp in the case isn't going up those fans will not speed up. Does the controller have a temp setting? What are your system temps? Plus what is the CPU temp at Idle? You are running a water cool. That is a little high to me 70c under load. The CPU & the System temps are two different controllers. I might be wrong but they don't work together. If the CPU temp is going up it will not change the system temp or tell it to speed up the fans.
Also wanted to add to the mix of great answers... Based of the experience of many here... Any time a splitter is used, fan control is lost. Doesn't happen all the time, but we've seen this issue/complaint multiple times.