A bit of background ... I am a cash game player getting back in to poker, and want to start playing some MTTs as well. Right now I am profitable at 25NL on ACR and in the past have played up to 100NL profitably a few years ago.

I have played some low/micro stake MTTs in the past with some mixed results, probably about breakeven or slightly losing. Bought the From the Ground Up MTT course and I am about half way through the preflop part of the course.

My preflop ranges were bad before watching this course (much too tight) - but most of the other stuff I was already aware of (positional awareness, opponent tendencies, stack sizes, how to play with different types of opponents left to act).

At a cash game it's pretty easy for me to spot a fish, pretty much anyone limping is a fish and their VPIP/PFR stats are obvious. With MTTs being kind of foreign to me, I feel a bit lost identifying the fish. Obviously if someone open shoves a big stack in a spot that doesn't make sense, or does something crazy postflop, I'm marking them, but with open limping (outside of the SB and some short stack plays) I am not sure if it's a valid strat in MTTs or if I should be marking them right away as in cash.