Which brand of Munich are you using? It could be variations in the way the Munich is kilned. It would be interesting to sample a variety of Munich malts from different maltsters side by side, with and without decotion mash. One for @Drunkula to have a go atGot this mashing at the minute, pH was a bit high again at 5.7. I've noticed that (in my experience at least) Munich malt doesn't seem to be as acidic as the calculators say, the predicted pH was 5.4 which is quite a big difference. That's the third time I've seen this in Munich based brews and something I'll have to keep in mind in future.