I recently was changing some of my plumbing and decided to replumb my Eheim 2215 which I use to run water to a heat exchanger and back to the tank. In an effort to save a few bucks I just picked up 1/2" tubing from Home Depot and plumbed everything up. What I quickly realized is that the Eheim quick connect fittings do not tightly secure the 1/2" ID tubing. Since the plumbing for this setup requires ~15 feet of tubing I really didn't want to have to purchase all Eheim 12/16 tubing so I just purchased a few feet of Eheim 12/16 tubing and some 1/2" tubing couplers and hose clamps. This way I can use the Eheim tubing at all of the quick connect junctions and then transition to cheaper conventional tubing.
Moral of the story:
Eheim quick connect fittings perform better with Eheim specific or metric sized tubing.
Moral of the story:
Eheim quick connect fittings perform better with Eheim specific or metric sized tubing.