another solution is to plumb in a (lets say your return line is 1") 1"x1/2"x1" SLPxFNPTxSLP "T" fitting in the middle of your return line that runs horizontially above the water surface. In the threaded FNPT, screw in a locline MNPT adapter fitting and run a length of locline off of it that has a smaller flare nozzle spraying water out at the same level as the surface of the water in your display tank. This will aggitate the water surface for great oxygen exchange, not splash much at all, and break any siphon. because the water flow goes straight through the "T" fitting easily, not much flow will exit the restricted locline that exits the "T" fitting at a 90 degree angle, but enough return water will exit to cause surface aggitation, and its easy to position at the right return height to pretent siphon and excess splashing...
Hope that helps you out.
Ive plumbed hundreds of display tanks, learned a few tricks along the way...