Hmm, I've got one of those tanks and I have not noticed your problems. I agitate every 30 sec for 5 sec. Typically I gently rock holding opposite corners, then with the next agitation it sits flat on the sink and I gently swivel it back and forth. Alternate back and forth through the development time. So far only trouble with the tank was when I tried to get by with 48 oz of developer rather than 1.5 liters. They are not the same! Sly