My cooling loop includes 2 High Flow Next (HFN) flow sensors. The HFN are separated by several devices so any turbulence generated by either one should not affect the other one. I have been running distilled water treated with Primochill Liquid Utopia. The 2 HFN always reported flow rates within 1% of each other - a testament to their accuracy.

Today I drained the distilled water and filled the loop with DP Ultra. In both HFN Flow Rate sensors I changed the Medium from Distilled Water to DP Ultra. Connector Types are both set to Inner Diameter >7mm. Now the difference in flow rates reported by the 2 HFN is about 5% instead of 1%. Is the High Flow Next less accurate with DP Ultra than with Distilled Water?

Also, the HFN manual says flow direction does not matter. When I put the loop back together, HFN #1 had coolant entering the left side but HFN #2 had coolant entering the right side. The flow rate difference in this condition was ~12%. I flipped HFN #2 around so coolant enters the left side. The flow rate difference dropped to 5%. Why would this happen if flow direction does not matter?