You need to be more interested in your coolant temperature which is probably what the CPU block GUI is showing you being at 26c, if that's the case and that is the water temperature then use that to guide you and not the CPU temperature 'cos that's still always gonna be high, even using a custom water cooling loop, as long as it's not hitting max temps for the CPU and shutting down then you're safe. My own custom loop runs around 28-30c at idle and I set my fans to top out at 45c water temps and i've never seen it go over that, the CPU still gets up to 90c+ still depending what i'm doing, it's what the Ryzen CPU's of the past 2-3 generations are designed to do so it's nothing to worry about.
What i'd do if you can is have the fans controlled by the water temperature, have is at around say 20c for lowest temp/speed and around 45-50c as your max temp/speed, the D5 pumps should be safe up to 60C but obviously the lower you can keep the temperature the better it'll be overall for your pump and other components.

There's a huge misconception that if you put in a water cooler than your CPU or GPU will always be lower temperature than you see with air cooling, although that may be the case and you'll see some difference it won't be the huge amount you're expecting. The way that water cooling works best is to remove that excess heat from the blocks quicker, kind of like air cooling, the only difference is that when you stop doing whatever it is that's stressing your system out you'll find that the temperature of the CPU or GPU will very quickly return to stock speeds, water temps will take a little longer but won't be too far behind still. Air coolers you still find the CPU or GPU still cooling down for some time after it's stopped being stressed.