I have a 20gal InfuSsion mash tun as well that I am running recirculation through an electric HERMS system with the SS Brewtech recirculation manifold and I have also been running into efficiency "issues". Initially, my efficiency values were in the low 60's, but have started to trend upwards. From my research into the issue, there were some main variables such as mash pH, grind size/consistency, sparge speed, and other process issues (ie flowrates too high / channelling, temperature problems, mash bed too compact, too short of a mash, etc.). Since then, I've tried to be as consistent and deliberate with my process as possible to avoid variables (especially focusing on a consistent hour-long sparge). From there, I looked at some of the things that what I wasn't doing, ie checking mash pH or milling my own grain. I started with checking mash pH and since I've done this, the efficiencies have increased to around 75% without changing anything else. My next step will be milling my own grain (or consistently sourcing them from the same place). As I was buying pre-milled grains online from a number of different places, this has been an uncontrollable variable. Another uncontrolled variable is that I'm not brewing the same beer every brew day, but I don't think that's going to change anytime soon (I like variety). While I'm far from where I want to be, I'm just going through the process as iteratively as possible. Hope this helps!
