My guess is that Tri-x has a thicker emuslion that the other two films.(posted 8399 days ago)
Try this: Instead of running the 30 degree water directly into the tank, stand the tank of 20 degree water in a bath of water at 30 degrees for 5 or 10 minutes, and let it gradually come up to temperature. Water poured very slowly into a cooler bath will 'laminate', and form a warmer layer, rather than mix properly.
Using a hardening fixer would probably be an equally good answer.