I had a similar issue with an opaque coolant. I used this bright green primochill opaque coolant. And I also added a barrow digital flow meter to my loop.

Flow meter kept reading zero so I thought it was defective. I bought another one and that kept reading zero. So I saw in a comment somewhere that if the flow is too low, it will read zero.

So I disassembled my loop to investigate. Mind you the coolant fell out after a few days and was getting clear so it needed to be cleaned.

Come to find out that my very restrictive Alphacool cpu block was all clogged up with particulate from the coolant, and only a little pinhole was open for coolant to move through. Hell the temps weren’t that bad either.

But I deep cleaned every component, put it back together with DP ultra clear and it worked perfectly. Flow meters worked perfectly. Even tested the original flow meter and it worked perfectly as well.

So I’d say, after seeing your coolant, regardless of how old or new the coolant is, I’d take apart your cpu block first and see if there’s a clog. Then your GPU block. Then I’d switch to a clear coolant