I've been using a Tetanol C41 home developing kit with nice results so far after approx 16 rolls of film (120 and 35mm). The instructions make no mention of agitation so I've been agitating for the first 30secs and then leaving the hand tank to stand for the remainder of the time (3:15 total for dev, 4min total for BLX). Is this correct or should I be agitating every minute?

Recently I've noticed some faint streaks on some frames (portraits with plain con tone background behind the subject) and I'm wondering if this is due to lack of agitating.