overall, I would jamming is more an operation problem than a design problem. As stated by Henry Bowman said, when the pH gets too low, the media becomes destabilized, and turns to "mud", which jams the unit. No matter what brand you have, this principal applies. Some media may be better at staying stable than others, but I believe it is all in how you set it up, and operate the equipment. By the way, I run a MRC CR-2 with spray bar. No flaws.